doveadm force-resync repair mailbox: (enhancement)

[jrse]

Currently rbox-force resync: scans the ceph storage for objects and compares them with the mail entries in index file.

This is done for all User mailboxes (ignoring the dovadm rmb force-resync mailbox param). The ceph operation to list all objects in a namespace is very costly. This listing of object is currently done for ech mailbox seperately.

enhancement: Do the scan for user objects once and use this list of objects to restore the index.

[jrse]

more tests under heavy load required to see if this optimization needs to be implemented. removing it from project scope.