rgw/restore: Persistently store the restore state for cloud-s3 tier

rgw/restore: Persistently store the restore state for cloud-s3 tier

In order to resume IN_PROGRESS restore operations post RGW service
restarts, store the entries of the objects being restored from `cloud-s3`
tier persistently. This is already being done for `cloud-s3-glacier`
tier and now the same will be applied to `cloud-s3` tier too.

With this change, when `restore-object` is performed on any object,
it will be marked RESTORE_ALREADY_IN_PROGRESS and added to a restore FIFO queue.
This queue is later processed by Restore worker thread which will try to
fetch the objects from Cloud or Glacier/Tape S3 services. Hence all the
restore operations are now handled asynchronously (for both `cloud-s3`,
`cloud-s3-glacier` tiers).

Signed-off-by: Soumya Koduri <skoduri@redhat.com>