Merge pull request #7786 from ceph/wip-rgw-indexless

rgw: indexless buckets (Yehuda Sadeh)

 - can define a policy, for which buckets are indexless
 - users can then create buckets under the specified placement target
 - indexless buckets will not be synced across zones
 - does not work with (s3) versioned buckets

Reviewed-by: Matt Benjamin <mbenjamin@redhat.com>
Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>