bug: correctly infer namespace of HTTPRoute backendRef

[solmonk]

To reproduce

Create gateway in default, service in non-default namespace.

Create the following httproute in non-default namespace:

apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: inventory
spec:
  parentRefs:
  - name: my-hotel
    namespace: default
    sectionName: http
  rules:
  - backendRefs:
    - name: inventory-ver1
      kind: Service
      port: 8090
      weight: 10

Current behavior

This leads to the following error when registering targets:

I0515 19:08:07.547245   87545 model_build_targets.go:107] errmsg: Build Targets failed because K8S service default/inventory-ver1 does not exist
I0515 19:08:07.547252   87545 model_build_targetgroup.go:162] Error buildTargets for backend ref service {{{0xc000b5c3b0 0xc000b5c3c0 inventory-ver1 <nil> 0xc000bbf240} 0xc000bbf244} []}

Seems the controller infers default namespace by default. example1 example2

What to expect

Since the route itself is in non-default namespace, the backendRefs should also implicitly refer to non-default.

Related

Possibly related to #244