Definition of KongCustomEntity CRD

[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 need to define the KongCustomEntity CRD to define a custom Kong entity that KIC does not support yet.

Proposed Solution

• Add CRD KongCustomEntity to define type, fields and attached object (plugin)
• Add CEL level validations on the CRD, like non-empty and immutable entity types

Additional information

No response

Acceptance Criteria

• A KongCustomEntity CRD is defined in KIC to specify a custom Kong entity.