Automatic merge from submit-queue (batch tested with PRs 50531, 50853, 49976, 50939, 50607)
Do not allow empty topology key for pod affinities.
**What this PR does / why we need it**:
This PR do not allow empty topology key for all 4 pod affinities.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
**Special notes for your reviewer**:
**Release note**:
```release-note
Affinity in annotations alpha feature is no longer supported in 1.8. Anyone upgrading from 1.7 with AffinityInAnnotation feature enabled must ensure pods (specifically with pod anti-affinity PreferredDuringSchedulingIgnoredDuringExecution) with empty TopologyKey fields must be removed before upgrading to 1.8.
```
@kubernetes/sig-scheduling-bugs @bsalamat @davidopp
0f8eaa45dd