Ensure that all supported Kubernetes resources fallback is covered in tests

[czeslavo]

Make sure that all Kubernetes resource kinds supported by KIC are covered in the fallback configuration tests. A preferable type of test that will allow simulating any object kind rejection on the Gateway side is an envtest with mocked Kong Admin API server. These tests could also generate golden files with the generated fallback configuration so that we can use them in another test ensuring this configuration gets accepted by a real Gateway instance.

Besides the envtests covering all possible objects, there should also exist an integration test that triggers a well-known failure (e.g. misconfiguring a Service) and ensures the fallback configuration is delivered to the Gateway as expected (turning off webhook validations can be leveraged to enable triggering some cases).

Please also ensure that if a Gateway rejects the generated fallback configuration, KIC will behave as expected (use the last valid config if it was preserved).

Blocked by #5931.

Tasks

Beta Give feedback

1. Implement KongClient integration test verifying fallback configuration propagation #6076
   0 of 23
   release/required +1
   
2. Implement an isolated integration test covering fallback configuration propagation #6077
   release/required +1