rgw/cloud-restore: Support restoration of objects transitioned to Glacier/Tape endpoint

rgw/cloud-restore: Support restoration of objects transitioned to Glacier/Tape endpoint

Restoration of objects from certain cloud services (like Glacier/Tape) could
take significant amount of time (even days). Hence store the state of such restore requests
and periodically process them.

Brief summary of changes

* Refactored existing restore code to consolidate and move all restore processing into rgw_restore* file/class

* RGWRestore class is defined to manage the restoration of objects.

* Lastly, for SAL_RADOS, FIFO is used to store and read restore entries.

Currently, this PR handles storing state of restore requests sent to cloud-glacier tier-type which need async processing.
The changes are tested with AWS Glacier Flexible Retrieval with tier_type Expedited and Standard.

Reviewed-by: Matt Benjamin <mbenjamin@redhat.com>
Reviewed-by: Adam Emerson <aemerson@redhat.com>
Reviewed-by: Jiffin Tony Thottan <thottanjiffin@gmail.com>
Reviewed-by: Daniel Gryniewicz <dang@redhat.com>
Signed-off-by: Soumya Koduri <skoduri@redhat.com>
(cherry picked from commit ef96bb0d6137bacf45b9ee2f99ad5bcd8b3b6add)