Add 1.20 Release Notes shadows to groups
Add 1.20 Release Notes shadows to groups

This adds all four release notes shadows on the 1.20 Kubernetes release
team to both the release team mailing list and the release team shadows
mailing list.

This is part of the release team shadow onboarding process.

thockin/k8s.io,thockin/k8s.io,kubernetes/k8s.io,thockin/k8s.io,kubernetes/k8s.io,kubernetes/k8s.io,kubernetes/k8s.io,thockin/k8s.io