Merge PR #35697 into master

Merge PR #35697 into master

* refs/pull/35697/head:
	doc: document cephfs mirroring developement status
	cephfs-mirror: cephfs-mirror daemon
	cephfs-mirror: FSMirror class to synchronize directory snaps
	common: introduce configuration options for cephfs-mirror daemon
	cephfs-mirror: InstanceWatcher class to register mirror instance
	cephfs-mirror: MirrorWatcher class to watch cephfs-mirror object
	cephfs-mirror: Watcher class to receive/ack watch notifications
	cephfs-mirror: ClusterWatcher class for watching peer changes
	librados: add API for fetching client addrs
	common: add cephfs_mirror subsystem
	cephfs-mirror: filesystem specification class

Reviewed-by: Patrick Donnelly <pdonnell@redhat.com>