Avoids performing lookups and producer registration on all partitions of a partitioned
topic when using SinglePartition routing without keyed messages

Lazy producers connect on demand on their first message.
The send timeout timer must be started on the first
message as there is no guarantee the connection will
complete

Ensure that the state is checked always in
PartitionedProducer::sendAsync to avoid buffering of
messages after closeAsync called.

Removed sequential locking in ProducerImpl::
handleCreateProducer that allowed for state to go
back to Ready after closeAsync called.

In order to ensure than authz errors are returned
during producer creation, start one producer
eagerly when using lazy partitioned producers.
When UseSinglePartition mode is used, the
eagerly created producer will be the only producer
created (when non-keyed messages are sent).

In the case that an internal producer is created
lazily and it fails, then fail any pending
requests immediately.