SectionNames should not collide

[kate-osborn]

An HTTPRoute can reference multiple Gateways in spec.ParentRefs, and the section names for the Gateways may be the same. For example:

apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: cafe
spec:
  parentRefs:
  - name: gateway-1
    sectionName: http
 - name: gateway-2
    sectionName: http
  hostnames:
  - "cafe.example.com"
  rules:
...

When we build the routes for the graph we assume that the section names are unique across all Gateways in the ParentRefs. This could lead to configuration errors and incomplete statuses.

Acceptance Criteria:

• Handle section name collision. Report status and build configuration for all section names that are the same across Gateways. Provided that the Gateway exists.
• Resolve FIXME: https://github.com/nginxinc/nginx-kubernetes-gateway/blob/52fab05f8455ad9d9c0f08a11c0dd6e992b5a797/internal/state/graph/httproute.go#L156

Aha! Link: https://nginx.aha.io/features/NKG-68