feat: add Ksql warning to KsqlResource response when CommandRunner degraded

[stevenpyzhang]

ksql> show streams;

 Stream Name         | Kafka Topic                 | Format 
------------------------------------------------------------
 KSQL_PROCESSING_LOG | default_ksql_processing_log | JSON   
 TEST                | TEST                        | JSON   
 TEST1               | TEST1                       | JSON   
------------------------------------------------------------
WARNING: The server has encountered an incompatible entry in its log and cannot process further DDL statements.
This is most likely due to the service being rolled back to an earlier version.

Done by adding a KsqlWarning to the existing warnings list for each KsqlEntity returned from the server.

Alternatively, we could just add a separate WarningEntity to the KsqlEntityList returned from the server instead of modifying each KsqlEntity.
https://github.com/confluentinc/ksql/blob/453125c87f8538f80029278f323c2c193870fa85/ksqldb-rest-model/src/main/java/io/confluent/ksql/rest/entity/WarningEntity.java

Testing done

Manual and unit test

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 #")

[agavra]

LGTM - I think it makes sense to add this to every statement so that it's clear what's going on. Might want to get one more opinion on this (perhaps from product)