Support custom entities in last known good configuration

[randmonkey]

Is there an existing issue for this?

• I have searched the existing issues

Does this enhancement require public documentation?

• I have added an Acceptance Criteria item for adding and/or adjusting public documentation (if applicable)

Problem Statement

Split from #4556 .
We do not have the method to fetch custom entities from Kong raw state. To support back filling custom entities from last good known config from Kong gateway, we need to parse and fill custom entities (entities not directly supported) in config fetcher. This needs go-database-reconciler to support custom entities.

Proposed Solution

• Support dumping custom entities from Kong gateway in go-database-reconciler
• Dump custom entities from Kong raw state fetched from Kong gateway in last good config
• Load last good config with custom entities when applying config failed

Additional information

No response

Acceptance Criteria

• KIC can dump custom entities to KongState structure from Kong raw state fetched from Kong gateway
• KIC can apply config with custom entities stored in last known good config when applying Kong config fails.

[randmonkey]

Mark it as blocked since this needs go-database-reconciler to support dumping custom entities.
Blocked by: Kong/go-database-reconciler#110.