Ensure uniqueness of generated locations

[pleshakov]

Describe the bug

For advanced content based routing, NKG generated auxiliary location for each match. However, those generated locations can clash with regular locations defined in an HTTPRoute and cause unintended behavior.

To Reproduce

1. Deploy NGF
2. Create gateway
3. Create coffee app
4. Create the following HTTPRoute:

apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: coffee
spec:
  parentRefs:
  - name: gateway
    sectionName: http
  hostnames:
  - "cafe.example.com"
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /coffee_prefix_route0
    backendRefs:
    - name: coffee-v1-svc
      port: 80
  - matches:
    - path:
        type: PathPrefix
        value: /coffee
      headers:
      - name: version
        value: v2
    backendRefs:
    - name: coffee-v2-svc
      port: 80

Get /coffee with header "version:v2" :

curl --resolve cafe.example.com:$GW_PORT:$GW_IP http://cafe.example.com:$GW_PORT/coffee -H "version:v2"

Should get response from coffee-v2, however the response comes from coffee-v1:

Server name: coffee-v1-58f4c685db-6djfc
Date: 15/Dec/2023:20:05:01 +0000
URI: /coffee
Request ID: 466b32ecd006ed8d9cdff2cbb5e8afeb

Expected behavior

• If a regular location clashes with an internal location, an error is reported that alerts the user of the specific issue.

The generated config (excerpts):

    location /coffee_prefix_route0 {...}

    location /coffee/ {...}

    location = /coffee {...}

    location /coffee_prefix_route0/ {...}

    location = /coffee_prefix_route0 {...}

Your environment

• Version of the NGINX Kubernetes Gateway - latest edge {"level":"info","ts":"2023-02-13T19:29:27Z","msg":"Starting NGINX Kubernetes Gateway","version":"0.1.0-rc.1-SNAPSHOT-1ee6b14","commit":"1ee6b14e09f9cd2bbf825f17a052b62749ce3ce2","date":"2023-02-13T18:44:39Z"}

[kate-osborn]

When fixing this bug, make sure to resolve this FIXME: https://github.com/nginxinc/nginx-kubernetes-gateway/blob/52fab05f8455ad9d9c0f08a11c0dd6e992b5a797/internal/nginx/config/validation/http_njs_match.go#L40

[mpstefan]

Additional Acceptance Criteria:

• Update internal locations to generate with a new prefix.
• Generated prefix is documented.