osd,crimson/osd: maintain pg_committed_to on replica rather than min_last_complete_ondisk

osd,crimson/osd: maintain pg_committed_to on replica rather than min_last_complete_ondisk

This commit updates the bulk of the interface pathways in crimson and
classic to refer to pg_committed_to rather than min_last_complete_ondisk
and changes the replica side to maintain pg_committed_to instead.

This commit shouldn't actually cause any behavior change -- we're still
passing min_last_complete_ondisk (which is a valid lower bound for
pg_committed_to!).

Signed-off-by: Samuel Just <sjust@redhat.com>