NIFI-16283 Support changing Connector versions

[markap14]

https://issues.apache.org/jira/browse/NIFI-16283

Summary

• support changing Connector bundle versions through the REST API, web UI, and toolkit CLI
• migrate Connector configuration and managed flow state while replacing the implementation
• create a GhostConnector when the target implementation cannot be instantiated
• add audit records, available-version metadata, and end-to-end system-test coverage

Testing

• framework Connector node and reload unit tests
• web API facade, DAO, DTO, and audit unit tests
• toolkit CLI unit tests
• Connector frontend and shared utility unit tests and lint
• ConnectorChangeVersionIT
• Checkstyle and PMD for affected Java modules

All listed tests passed before rebasing onto the main branch version change to 2.13.0-SNAPSHOT. A post-rebase local Maven run could not begin compilation because the local Maven repository does not yet contain the new 2.13.0-SNAPSHOT reactor artifacts; CI will build those artifacts from the full reactor.