Merge pull request #41617 from timothysc/affinity_annotations_flaggate

Automatic merge from submit-queue (batch tested with PRs 39373, 41585, 41617, 41707, 39958)

Feature-Gate affinity in annotations 

**What this PR does / why we need it**:
Adds back basic flaggated support for alpha Affinity annotations

**Special notes for your reviewer**:
Reconcile function is placed in the lowest common denominator, which in this case is schedulercache, because you can't place flag-gated functions in apimachinery. 

**Release note**:

```
NONE
```

/cc @davidopp

staging/src/k8s.io/apiserver/pkg/util/feature/feature_gate.go

@@ -107,6 +107,11 @@ type FeatureGate interface {
 	// owner: @pweil-
 	// alpha: v1.5
 	ExperimentalHostUserNamespaceDefaulting() bool
+
+	// owner: @davidopp
+	// alpha: v1.6
+	// TODO: remove when alpha support for affinity is removed
+	AffinityInAnnotations() bool
 }
 
 // featureGate implements FeatureGate as well as pflag.Value for flag parsing.