rgw/dbstore: Fix crash in delete_stale_objs

[soumyakoduri]

Fix a race between RemoveBucket and delete_stale_objs operations
by using shared_ptr to add reference to DB Ops.

Fixes:https://tracker.ceph.com/issues/55828
Signed-off-by: Soumya Koduri skoduri@redhat.com

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[soumyakoduri]

http://pulpito.front.sepia.ceph.com/soumyakoduri-2022-06-24_03:21:53-rgw:dbstore-wip-skoduri-dbstore-fix-distro-default-smithi
http://pulpito.front.sepia.ceph.com/soumyakoduri-2022-06-24_03:18:57-rgw-wip-skoduri-dbstore-fix-distro-default-smithi/