WHAT

Implement the Non-breaking changes for admin server

WHY

Increase consistency between the Kafka instance admin API and other public APIs

Copied from MGDSTRM-4891.

Non-breaking

1. Add new fields to `Error` [1], provide endpoints to fetch errors, full list and individually
2. Add `ObjectReference` type [2], all singular API types should extend (`id` will not be required/available for some types)
3. Add `List` type [3], all collection API types should extend

Breaking (wait for major version change)

1. Change to snake case property names
2. Snake case for URL/path segments
3. Change of `code` field from integer to string in `Error` Object

[1] https://github.com/redhat-developer/app-services-api-guidelines/tree/main/spectral#rhoas-error-schema
[2] https://github.com/redhat-developer/app-services-api-guidelines/tree/main/spectral#rhoas-object-schema
[3] https://github.com/redhat-developer/app-services-api-guidelines/tree/main/spectral#rhoas-list-schema