sig-release: Update Prow plugin configs
sig-release: Update Prow plugin configs

- Update note about temporary blockade in k/rel
  We should continue to consider the blockade on release tooling changes
  permanent until they are completely replaced by krel and kubepkg
- Enable plugins for k/release and k/sig-release:
  - mergecommitblocker
  - release-note (k/rel only)
  - require-matching-label
- Configure k/release and k/sig-release to require kind and priority
  labels for PRs and issues

Signed-off-by: Stephen Augustus <f96984fef9637085f0559f1484dfd4e99545cd6e@vmware.com>

monopole/test-infra,cjwagner/test-infra,cblecker/test-infra,BenTheElder/test-infra,jessfraz/test-infra,pwittrock/test-infra,pwittrock/test-infra,cjwagner/test-infra,kubernetes/test-infra,jessfraz/test-infra,pwittrock/test-infra,BenTheElder/test-infra,ixdy/kubernetes-test-infra,cblecker/test-infra,brahmaroutu/test-infra,dims/test-infra,cblecker/test-infra,dims/test-infra,michelle192837/test-infra,ixdy/kubernetes-test-infra,pwittrock/test-infra,cjwagner/test-infra,brahmaroutu/test-infra,michelle192837/test-infra,monopole/test-infra,kubernetes/test-infra,michelle192837/test-infra,michelle192837/test-infra,fejta/test-infra,jessfraz/test-infra,BenTheElder/test-infra,pwittrock/test-infra,BenTheElder/test-infra,fejta/test-infra,cblecker/test-infra,michelle192837/test-infra,kubernetes/test-infra,fejta/test-infra,jessfraz/test-infra,ixdy/kubernetes-test-infra,brahmaroutu/test-infra,kubernetes/test-infra,BenTheElder/test-infra,dims/test-infra,cjwagner/test-infra,jessfraz/test-infra,dims/test-infra,fejta/test-infra,monopole/test-infra,monopole/test-infra,kubernetes/test-infra,monopole/test-infra,cblecker/test-infra,kubernetes/test-infra,brahmaroutu/test-infra,dims/test-infra,brahmaroutu/test-infra,cblecker/test-infra,jessfraz/test-infra,fejta/test-infra,BenTheElder/test-infra,cjwagner/test-infra,cjwagner/test-infra,monopole/test-infra,brahmaroutu/test-infra,ixdy/kubernetes-test-infra,ixdy/kubernetes-test-infra,michelle192837/test-infra,fejta/test-infra,dims/test-infra