Fix Javadoc warnings

[fpj]

Problem description
Fix Javadoc warnings currently showing up when building.

Problem location
Javadoc.

Suggestions for an improvement
Fix the Javadoc warnings.

[fpj]

> Task :client:generateJavadoc
/Users/fpj/code/pravega-schema-registry/client/build/delombok/io/pravega/schemaregistry/client/SchemaRegistryClientConfig.java:93: warning: no @return
    public URI getSchemaRegistryUri() {
               ^
1 warning

> Task :contract:generateJavadoc
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/CodecType.java:106: warning: no @return
    public String getName() {
                  ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/CodecType.java:119: warning: no @return
    public ImmutableMap<String, String> getProperties() {
                                        ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/Compatibility.java:248: warning: no @return
    public Type getType() {
                ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/EncodingId.java:64: warning: no @return
    public int getId() {
               ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/EncodingInfo.java:58: warning: no @return
    public VersionInfo getVersionInfo() {
                       ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/EncodingInfo.java:67: warning: no @return
    public SchemaInfo getSchemaInfo() {
                      ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/EncodingInfo.java:76: warning: no @return
    public CodecType getCodecType() {
                     ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/GroupHistoryRecord.java:72: warning: no @return
    public SchemaInfo getSchemaInfo() {
                      ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/GroupHistoryRecord.java:81: warning: no @return
    public VersionInfo getVersionInfo() {
                       ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/GroupHistoryRecord.java:90: warning: no @return
    public Compatibility getCompatibility() {
                         ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/GroupHistoryRecord.java:98: warning: no @return
    public long getTimestamp() {
                ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/GroupHistoryRecord.java:107: warning: no @return
    public String getSchemaString() {
                  ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/GroupProperties.java:139: warning: no @return
    public SerializationFormat getSerializationFormat() {
                               ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/GroupProperties.java:148: warning: no @return
    public Compatibility getCompatibility() {
                         ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/GroupProperties.java:157: warning: no @return
    public boolean isAllowMultipleTypes() {
                   ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/GroupProperties.java:166: warning: no @return
    public ImmutableMap<String, String> getProperties() {
                                        ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/SchemaInfo.java:148: warning: no @return
    public String getType() {
                  ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/SchemaInfo.java:157: warning: no @return
    public SerializationFormat getSerializationFormat() {
                               ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/SchemaInfo.java:166: warning: no @return
    public ByteBuffer getSchemaData() {
                      ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/SchemaInfo.java:175: warning: no @return
    public ImmutableMap<String, String> getProperties() {
                                        ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/SchemaWithVersion.java:82: warning: no @return
    public SchemaInfo getSchemaInfo() {
                      ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/SchemaWithVersion.java:91: warning: no @return
    public VersionInfo getVersionInfo() {
                       ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/VersionInfo.java:102: warning: no @return
    public String getType() {
                  ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/VersionInfo.java:110: warning: no @return
    public int getVersion() {
               ^
/Users/fpj/code/pravega-schema-registry/contract/build/delombok/io/pravega/schemaregistry/contract/data/VersionInfo.java:119: warning: no @return
    public int getId() {
               ^
25 warnings

> Task :serializers:generateJavadoc
/Users/fpj/code/pravega-schema-registry/serializers/build/delombok/io/pravega/schemaregistry/serializers/SerializerConfig.java:350: warning: no @return
    public String getGroupId() {
                  ^
/Users/fpj/code/pravega-schema-registry/serializers/build/delombok/io/pravega/schemaregistry/serializers/SerializerConfig.java:358: warning: no @return
    public String getNamespace() {
                  ^
/Users/fpj/code/pravega-schema-registry/serializers/build/delombok/io/pravega/schemaregistry/serializers/SerializerConfig.java:368: warning: no @return
    public boolean isRegisterSchema() {
                   ^
/Users/fpj/code/pravega-schema-registry/serializers/build/delombok/io/pravega/schemaregistry/serializers/SerializerConfig.java:379: warning: no @return
    public boolean isRegisterCodec() {
                   ^
/Users/fpj/code/pravega-schema-registry/serializers/build/delombok/io/pravega/schemaregistry/serializers/SerializerConfig.java:387: warning: no @return
    public Encoder getEncoder() {
                   ^
/Users/fpj/code/pravega-schema-registry/serializers/build/delombok/io/pravega/schemaregistry/serializers/SerializerConfig.java:399: warning: no @return
    public Decoders getDecoders() {
                    ^
/Users/fpj/code/pravega-schema-registry/serializers/build/delombok/io/pravega/schemaregistry/serializers/SerializerConfig.java:416: warning: no @return
    public boolean isFailOnCodecMismatch() {
                   ^
/Users/fpj/code/pravega-schema-registry/serializers/build/delombok/io/pravega/schemaregistry/serializers/SerializerConfig.java:431: warning: no @return
    public boolean isWriteEncodingHeader() {
                   ^
8 warnings

> Task :server:generateJavadoc
/Users/fpj/code/pravega-schema-registry/server/build/delombok/io/pravega/schemaregistry/storage/impl/group/records/TableRecords.java:1549: warning: no @return
        public SchemaInfo getSchemaInfo() {
                          ^
/Users/fpj/code/pravega-schema-registry/server/build/delombok/io/pravega/schemaregistry/storage/impl/schemas/SchemaRecords.java:672: warning: no @return
        public SchemaInfo getSchemaInfo() {
                          ^
2 warnings