Add system test for reconciling resources

[kate-osborn]

Is your enhancement request related to a problem? Please describe.
We do not currently test the k8s controller's reconciling logic that filters out resource events. For example, resources that have a generation field should not be reconciled when that generation has not changed. See #1422 for more details on how this works.

What would you like to be added:
A functional test that ensures we don't reconcile resource events that do not contain any updates to the NGINX configuration.
This test would involve making changes to resources that aren't material to NGF (e.g. updating the labels of an HTTPRoute) and verifying the following:

1. The controller did not reconcile the resource. This can be verified through the controller_runtime_reconcile_total prometheus metric.
2. The nginx configuration was not updated. This can be verified by checking the nginx configuration version.

Why this is needed:
To cover untested functionality of NGF.