rgw/logging: deleteting the object holding the temp object name on cleanup

rgw/logging: deleteting the object holding the temp object name on cleanup

* in case of prefix per source this would prevent leaking this object
* in case of share prefix, it would prevent data loss when other source
buckets will try to commit an already comitted temporary object
* when updatign the "last committed" attribute, the object must exist.
  this is so that commit without rollover (in case of cleanup) won't
  recreate the deleted object
* some refactoring of try-catch code to have less nesting

Fixes: https://tracker.ceph.com/issues/73675
Signed-off-by: Yuval Lifshitz <ylifshit@ibm.com>