GRPCRoute Conformance Test for BackendRef Weight Traffic Splitting

[mpstefan]

As a implementer of the Kubernetes Gateway API
I want a conformance test to cover the backendref weight traffic splitting feature for GRPCRoute
So that I can ensure my implementation matches the functionality intended of the Gateway API.

Ask in Gateway API Slack channel if they would accept this contribution. May want to reach out to current assignee.

Acceptance

• A conformance test is created to test the functionality of the backendref weight traffic splitting for NGF.
• The conformance test is submitted to the Gateway API.

[pleshakov]

kubernetes-sigs/gateway-api#2901