Automatic merge from submit-queue (batch tested with PRs 54107, 54184, 54377, 54094, 54111). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

add e2e tests for NEG

This PR includes tests:
- ingress conformance test
- scaling up and down backends
- switching backend between IG and NEG
- rolling update backend should not cause service disruption

```release-note
NONE
```