Support traffic splitting for TLSRoutes

[kate-osborn]

Add support for TlsRouteRule.BackendRef.Weight which would allow users to configure traffic splitting for TLSRoutes.

Notes:

• this is an extended feature
• TLSRoute has undefined behavior when multiple TLSRouteRules are specified. We need to figure out the desired behavior in that case before implementing this feature. For example what is the expected behavior for the following TLSRoute:

apiVersion: gateway.networking.k8s.io/v1alpha2
kind: TLSRoute
metadata:
  name: tls-route-confusion
spec:
  parentRefs:
  - name: gateway-tlsroute
  hostnames:
  - abc.example.com
  rules:
  - backendRefs:
    - name: tls-backend
      port: 443
  - backendRefs:
    - name: tls-backend-2
      port: 443 

[github-actions]

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