PGLog: store extra duplicate ops beyond the normal log entries

PGLog: store extra duplicate ops beyond the normal log entries

This helps us avoid replaying non-idempotent client operations when
the pg log is very short, e.g. in an effort to force OSDs to use
backfill rather than regular recovery. This can be advantageous to
avoid blocking i/o to objects, at the cost of longer total time to
become clean (since backfill requires scanning the objects to see what
is missing).

Signed-off-by: Josh Durgin <jdurgin@redhat.com>