Support appProtocol Field for HTTPBackendRef

[mpstefan]

As a user of NGF
I want appProtocol field to be supported for HTTPBackendRefs
So that I can ensure all traffic to my application is the protocol I expect.

Acceptance

• A BackendRef is marked as invalid if it refers to a Kubernetes Service that has an incompatible appProtocol for the given Route type.
• The "New Standard Protocols" as outlined in GEP-3726 are included:
  • 'kubernetes.io/h2c'
  • 'kubernetes.io/ws'
  • 'kubernetes.io/wss'
• If a Route is not able to send traffic to the backend using the specified protocol then the backend is considered invalid. Implementations MUST set the "ResolvedRefs" condition to "False" with the "UnsupportedProtocol" reason.

More info