Automatic merge from submit-queue (batch tested with PRs 49120, 46755, 49157, 49165, 48950)
kubectl: deduplicate deployment generators
**What this PR does / why we need it**: See the description on https://github.com/kubernetes/kubectl/issues/44
**Which issue this PR fixes**: fixes https://github.com/kubernetes/kubectl/issues/44
**Special notes for your reviewer**: Yes, the lines added and removed are about the same. This is because I added 20+ lines of docstrings. Check the diff. You'll see I deleted a lot of duplicated logic :)
**Release note**:
```release-note
NONE
```