rgw/notifications: send correct size in case of delete marker creation

rgw/notifications: send correct size in case of delete marker creation

Fixes: https://tracker.ceph.com/issues/51681
Signed-off-by: Yuval Lifshitz <ylifshit@redhat.com>
(cherry picked from commit d81e27faa1033c5290cfd0b4cf27cdaf98d34bc4)

Conflicts:
	src/rgw/rgw_op.cc
	src/test/rgw/bucket_notification/test_bn.py

Cherry-pick notes:
- src/test/rgw/bucket_notification/test_bn.py changes manually applied to src/test/rgw/rgw_multi/tests_ps.py for Pacific
- conflicts in rgw_op.cc due to rename of RGWObject to Object after Pacific