mgr/mirroring,tools/cephfs_mirror: Handle checkpoint state transition

When a new checkpoint is being added or when the daemon gets restarted,
it will check whether the newly created checkpoint or any other old
checkpoints have already been mirrored onto the remote peer. If so, it
will transition to the correct state by checking for the highest snap id
present on the remote, and setting all the checkpoints which have snap id
lesser than or equal to that of the remote to COMPLETE. This is done by
sending an acquire notification from the mirroring module to the mirror
daemon, which is handled in the add_directory path, by adding the directory
to be checked for the state transition in the tick thread.
This path gets triggered:
a) when the daemon gets restarted
b) when the peer mapping changes
c) by sending the acquire notification from checkpoint add/now CLIs.
d) when mirroring module restarts

Fixes: https://tracker.ceph.com/issues/73454
Signed-off-by: Karthik U S <karthik.u.s1@ibm.com>