Request for addition to 1.11 RC: GEODE-7454: Docs for Cluster Management Service

[Dave Barnes]

Docs for a feature that's already implemented - no code changes.
Can be cherry-picked from the develop branch as-is with no modifications.
https://github.com/apache/geode/commit/e48f34048c574440ed7e0640f42e9c82d789becb