Race Condition in Schema Register

[agavra]

At the moment, the rest-server will create the schema when it ensures the topics exist. This is done by building the logical plan from for the query using the snapshot of the metastore. However, it's possible that when the command is actually executed that one or more of the sources in the metastore have changed. This could result in a different schema - one out of whack with the schema in the SR!

See discussion for why we decided to commit anyway knowing this bug exists: #4717 (comment)