src/mon/PGMap.cc: check unfound obejcts in `get_unavailable_pg_in_pool_map`

src/mon/PGMap.cc: check unfound obejcts in `get_unavailable_pg_in_pool_map`

If a pool has any PG with unfound objects, we should consider
it unavailable for the availability score. If a PG has unfound
objects, it will be recorded in PGMap.

In `get_unavailable_pg_in_map`, if a PG has unfound obejcts,
we add it to `pool_pg_unavailable_map`.

Fixes: https://tracker.ceph.com/issues/67777
Signed-off-by: Shraddha Agrawal <shraddha.agrawal000@gmail.com>