mon/MgrMonitor: plug PAXOS for batched MgrMap/OSDMap

mon/MgrMonitor: plug PAXOS for batched MgrMap/OSDMap

Plugging PAXOS has the effect of batching map updates into a single
PAXOS transaction. Since we're updating the OSDMap several times and the
MgrMap, plug PAXOS for efficiency. This also has the nice effect of
reducing any delay between the active mgr getting dropped and the
blocklisting of its clients. This doesn't resolve any race condition as
the two maps are never processed in one unit. So the former active
manager may process the OSDMap blocklists before learning it is dropped
from the MgrMap.

Fixes: https://tracker.ceph.com/issues/58923
Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>