GRPCRoute Conformance Test for Request Header Filter

[mpstefan]

As a implementer of the Kubernetes Gateway API
I want a conformance test to cover the request header filter feature for GRPCRoute
So that I can ensure my implementation matches the functionality intended of the Gateway API.

Pre-reqs

• Ask if contributor is still interested in pursuing Add conformance test for GRPCRouteFilterRequestHeaderModifier kubernetes-sigs/gateway-api#2900 as we will be picking this up. This ticket has been auto-closed as not planned, but we don't think we need a new issue, we can just open a PR with the changes
• Ask in the Gateway Sig Slack channel if this is a welcome contribution.

Acceptance

• The conformance test is submitted to the Gateway API.
• The conformance test is added to test the functionality of the request header filter for NGF.

[pleshakov]

kubernetes-sigs/gateway-api#2900