Reconcile xRoutes when the Services they reference are modified

[nathancoleman]

Fixes #230

Changes proposed in this PR:

Re-reconcile HTTPRoutes and TCPRoutes when Kubernetes Service objects that the route(s) reference as backends are created, modified, or deleted.

How I've tested this PR:

1. Set up service(s) w/ backends using the Learn guide setup on Kind

2. Verify everything is working

   • https://localhost:8443 should bring up Hashicups
   • https://localhost:8443/echo should bring up echo service
   • The following should show the :8443 listener

     $ kubectl port-forward pod/<gateway_pod_name> 8081:19000
     $ curl localhost:8081/listeners

3. Delete all services referenced by HTTPRoutes

   $ kubectl delete service/echo-1 --namespace default
   $ kubectl delete service/echo-2 --namespace default
   $ kubectl delete service/nginx --namespace default

4. Verify that listener is removed from gateway

   • https://localhost:8443 should fail to bring up Hashicups
   • https://localhost:8443/echo should fail to bring up echo service
   • The following should show no :8443 listener

     $ kubectl port-forward pod/<gateway_pod_name> 8081:19000
     $ curl localhost:8081/listeners

5. Restore services

   $ kubectl apply -f two-services

6. Verify everything is working again after a few seconds for syncing

   • https://localhost:8443 should bring up Hashicups
   • https://localhost:8443/echo should bring up echo service
   • The following should show the :8443 listener

     $ kubectl port-forward pod/<gateway_pod_name> 8081:19000
     $ curl localhost:8081/listeners

How I expect reviewers to test this PR:

See above

Checklist:

• Tests added
• CHANGELOG entry added

  Run make changelog-entry for guidance in authoring a changelog entry, and
  commit the resulting file, which should have a name matching your PR number.
  Entries should use imperative present tense (e.g. Add support for...)

[nathancoleman]

Planning to add more test coverage next week

[mikemorris]

LGTM assuming currently-skipped test passes and adding the additional routes to the HTTP route controller tests still passes as expected.

Suggested changes for HTTP route controller apply to TCP route controller too.

[mikemorris]

TIL a use case for goto syntax that doesn't feel too gross.

[nathancoleman]

This is the old format which was replaced by the go:build format in go 1.17 (docs)