Automated conformance tests in pipeline

[mpstefan]

As a contributor to the NGINX Kubernetes Gateway project
I want to run the Gateway API conformance tests every time I create a pull request
So that we are validating that the NKG project is conformant with the Gateway API specification after every change we make to the project.

Acceptance

• Every merge on main and release branches triggers Gateway API conformance tests to be run on the code submitted.
• The Gateway API webhook is enabled on all tests.
• At least one test should be enabled and passing.
• Issues are created/validated to track remaining gaps for 'core' support.