osd_types: add last_peered, last_became_peered

Signed-off-by: Samuel Just <sam.just@inktank.com>
osd/: go "peered" instead of "active" when < min_size

In the case of a replicated pool, the pg will transition to "peered"
rather than "active", where it can perform backfill bringing itself up
to min_size peers.  To that end, most operations now require
is_peered rather than is_active (OSDOps being the primary exception).
Also, rather than using the query_epoch on the activation message as the
activation epoch (for last_epoch_started) on the replica, we instead
use the last_epoch_started in the info sent by the primary.  This
allows the primary to not advance last_epoch_started past the last
known actual activation.  This will prevent later peering epochs from
requiring the last_update from a peered epoch to go active (might be
divergent).  We do allow scrubbing while peered.

Fixes: #7862
Signed-off-by: Samuel Just <sam.just@inktank.com>