schema-registry.schemaMeta is unpredictable

[PHaroZ]

Hi,

When schema-registry load a schema it had them into this.schemaMeta, keyed by the topic name schemaObj.topic. Unfortunately the content of schemaMeta is unpredictable if some topics also have a schema for their key.
Because 2 schemas are loaded for each topic - one for the value and one for the key - each of them are added to this.schemaMeta with the same topic name, so only the last one wins.

As this.schemaMeta doesn't seem to be used by kafka-avro I suggest to only add value schema in this.schemaMeta: this is what it's suggested by the comment on this.schemaMeta .