Automatic merge from submit-queue (batch tested with PRs 65301, 65291, 65307, 63845, 65313). 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 client-go example using fake client in test.

**What this PR does / why we need it**:

This adds an example showing the steps needed to get a working
SharedInformerFactory with a fake client for testing.


**Special notes for your reviewer**:
I had a really hard time figuring out how to use this utility correctly. I don't think this example is sufficient documentation, but it's a good start.

**Release note**:

```release-note
NONE
```
/sig api-machinery
/kind documentation