ProtobufConverter fromConnectData doesn't honour existing field ids in SR

When source is Avro and destination is Proto if a new field is added in the avro schema at the top or somewhere in the middle, and the connector is restarted, then field ids are miss matched. This occurs because when generating the schema from the connect schema dynamically is it not taking into context the current/latest proto schema in SR and ensuring the field id is not used (typically increment from last highest).

Start by tracing ProtobufConverter.fromConnectData and how it reads the current/latest schema from Schema Registry when converting an Avro source schema to Proto. Reproduce the case where a field is inserted at the top or middle, then verify that existing field IDs remain unchanged and the new field receives an unused ID after connector restart.

Written by the indexing model from the issue text.