fix: clean up the cli

[Bento007]

Reason for Change

• configure logging when the cli is initialize, not when a specific command it called. This prevents us from configuring logging in multiple places. This has be an issue when using the cellxgene-schema library in the backend.
• use logger to ouput messages instead of print. This makes it easier to silence extra messages in our logs

Changes

• configure logging when the cli is initialize
• Use the schema_cli group to add new commands
• use logger to ouput messages instead of print.

Testing

• installed using make install locally and ran
  cellxgene-schema validate ./cellxgene_schema_cli/tests/fixtures/h5ads/example_valid.h5ad
  and
  cellxgene-schema -v validate ./cellxgene_schema_cli/tests/fixtures/h5ads/example_valid.h5ad
  and verified the log messages were as expected.

[ejmolinelli]

@Bento007 @joyceyan
This looks great - CLI should always use logger