sig-cluster-lifecycle: amend the SIG charter
sig-cluster-lifecycle: amend the SIG charter

- Remove ownership of the upgrade / downgrade testing of k8s.
Now owned by SIG Cloud Provider / GCP as it only supports
GCP clusters. See:
https://github.com/kubernetes/kubernetes/tree/master/test/e2e/cloud/gcp
- Remove the "lock-step" coordination with SIG-Release. Historically
the release waited for kubeadm to update its default k8s versions
constants after a "stable-1.x" label was created. No longer needed,
as kubeadm defaults to "stable-1":
https://github.com/kubernetes/kubernetes/blob/master/cmd/kubeadm/app/apis/kubeadm/v1beta2/defaults.go#L36
- Add note about release "informing/blocking" test jobs.
- Add sig-scheduling mention under "Out of scope".
- Add sig-apps mention under "Out of scope".

pwittrock/community,kubernetes/community,pwittrock/community,kubernetes/community,kubernetes/community