ceph-rgw: introduce rgw zone to the name schema

[clwluvw]

This is needed by ceph-exporter as it is parsing the socket by the number of dots. Although the rgw_zone variable is only used for constructing the client name and has nothing to do with multisiting. Reference: https://github.com/ceph/ceph/pull/52698

[Eli-Tarrago]

I have a multi-site rgw configured by ceph-ansible and I'm concerned this change doesn't address previously configured radosgw zones.

I agree this change is the proper way of configuring radosgw