Automatic merge from submit-queue (batch tested with PRs 55545, 55548, 55815, 56136, 56185). 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>.

Extend apiserver testserver

**What this PR does / why we need it**:
Extend the test pkg of api-server a little bit so that it can be used by others
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:
We wanted to use this test pkg while creating a new integration test fixture, the idea of starting the api-server without actually starting a proper etcd (integration etcd ) is very useful, if would be great to extend this for other usecases such as `insecure` mode too.

It will also be useful to get the working `tmpdir` returned so that we could store additional certs (such as service account public and private keys and kubeconf for this apiserver) if needed, which will be cleaned up automatically by the `teardownFn` when the api server is terminating.

**Release note**:

```release-note
NONE
```
ref: https://github.com/kubernetes/kubernetes/pull/50144