rgw/CloudTransition: Add new options to configure tier endpoint

rgw/CloudTransition: Add new options to configure tier endpoint

As mentioned in https://docs.google.com/document/d/1IoeITPCF64A5W-UA-9Y3Vp2oSfz3xVQHu31GTu3u3Ug/edit,
the tier storage class will be configured at zonegroup level.

So the existing CLI "radosgw-admin zonegroup placement add  <id> --storage-class <class>" will be
used to add tier storage classes as well but with extra tier-config options mentioned below -

--tier-type : "cloud"
--tier-config : [<key,value>,]

These tier options are already defined to configure cloud sync module which are being reused here.

TODO:
* Add multipart options (if any , like part size, threshold)
* Document
* Test upgrade/downgrade

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