feat: add a DefaultSchemaRegistryClient and remove default for SR url in KsqlConfig

[stevenpyzhang]

Description

Fixes #4319

Removed default URL for SR from KsqlConfig
Implemented a new DefaultSchemaRegistryClient that's used when the URL is ""

ksql> CREATE STREAM pageviews_avro WITH (KAFKA_TOPIC='pageviews', VALUE_FORMAT='AVRO');
Schema registry fetch for topic pageviews request failed.
Caused by: KSQL is not configured to use a schema registry. To enable it, please
        set ksql.schema.registry.url

Testing done

Unit test
Verified logs weren't being spammed when closing queries

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[rodesai]

LGTM. One comment inline.

[stevenpyzhang]

Reworked the error message to be pluggable with the ErrorMessages interface.

[stevenpyzhang]

While reworking this to have the pluggable error message, it seems like it might be better to move the config from KsqlRestConfig to KsqlConfig, thoughts @rodesai @spena ? Also, tagging @big-andy-coates since he was reviewer of original PR adding the config.

ErrorMessages seems generic enough to apply to any KSQL user case, not restricted to the rest application.

[rodesai]

LGTM

[vcrfxia]

Sorry I'm late to the party, but this is a breaking change, right? If I understand correctly, previously users didn't need to explicitly set a config for KSQL to pick up a Schema Registry cluster at localhost:8081 but now they do. We should:

• edit the git commit message or otherwise reflect this so it's picked up by the changelog
• loop in someone from devX to make sure we haven't broken demos/examples

[rodesai]

This change broke confluent-security-plugins. I've submitted a PR with a workaround (https://github.com/confluentinc/confluent-security-plugins/pull/257), but it's not a real fix to the problem because if a user uses RBAC they can no longer set a customized error message. I think we should either:

• move ErrorMessages to KsqlConfig and construct it correctly in confluent-security-plugins, or:
• refactor this change to have DefaultSchemaRegistryClient throw a custom exception without the special error message, and have the rest endpoint look out for this exception to set the final error message (like we do for auth errors).

My preference would be the latter since it keeps the usage of the Errors interface more isolated.