mon/MgrMap: dump last_failure_osd_epoch and active_clients at top level

mon/MgrMap: dump last_failure_osd_epoch and active_clients at top level

Currently last_failure_osd_epoch and active_clients are dumped in the
always_on_modules dictionary in "ceph mgr dump" output.  This goes back
to when these fields were added in commits f2986a4400bb ("mon/MgrMonitor:
blacklist previous instance") and df507cde8d71 ("mgr: forward RADOS
client instances for potential blacklist") but is wrong as these fields
have nothing to do with always-on modules.

Fixes: https://tracker.ceph.com/issues/58647
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
(cherry picked from commit 7b5e16130afc4b89c934fb95c805eb2e369cd29a)

Conflicts:
	PendingReleaseNotes [ moved to >=17.2.6 section ]