Inconsistent label/annotations names should follow K8s name conventions (aka. kebab-case)

[cardil]

Some labels/annotations used in Serving use kebab case like no-gc (see: https://knative.dev/docs/serving/revision-gc/#revision-garbage-collection), others use dot separator like ingress.class (see: https://knative.dev/docs/developer/serving/services/ingress-class/#using-the-ingress-class-annotation), and others use camel case like minScale (see: https://knative.dev/docs/serving/autoscaling/scale-bounds/#lower-bound).

Kubernetes has a naming convention for labels and annotations. It uses kebab case - see: https://kubernetes.io/docs/concepts/overview/working-with-objects/common-labels

Also, there's an issue #7300 which makes a similar change to config maps, so it adds to the inconsistency.

/area API
/area autoscale
/area networking

Expected Behavior

Knative should follow Kubernetes guidelines closely, and all annotations and labels should be renamed to be written in kebab case.

Actual Behavior

Some labels and annotations are using a different notation than others.

[dprotaso]

/assign @dprotaso