mgr/dashboard: grafana panels for rgw multisite sync performance

mgr/dashboard: grafana panels for rgw multisite sync performance

* RGW sync perf. counters are now exposed through grafana panels.
* Sync Performance tab is only shown if rgw realm is detected.
* Prometheus module: added metrics suitable for prometheus consumption (from existing ones, not replacing for backward compatibility).

Fixes: https://tracker.ceph.com/issues/45310
Signed-off-by: Alfonso Martínez <almartin@redhat.com>
(cherry picked from commit cf4ff7d2f03bc285a3fae3f27577333f11dab58a)

 Conflicts:
   - Solved conflicts from cherry-pick:
       src/pybind/mgr/dashboard/controllers/rgw.py
       src/pybind/mgr/dashboard/frontend/src/app/ceph/rgw/rgw-bucket-form/rgw-bucket-form.component.spec.ts
       src/pybind/mgr/dashboard/frontend/src/app/ceph/rgw/rgw-bucket-form/rgw-bucket-form.component.ts
       src/pybind/mgr/dashboard/frontend/src/app/ceph/rgw/rgw-daemon-list/rgw-daemon-list.component.ts
       src/pybind/mgr/dashboard/frontend/src/app/shared/api/rgw-site.service.spec.ts
       src/pybind/mgr/dashboard/frontend/src/app/shared/api/rgw-site.service.ts
       src/pybind/mgr/dashboard/services/rgw_client.py
       src/pybind/mgr/dashboard/tests/test_rgw_client.py
   - src/pybind/mgr/dashboard/tools.py: added method included in a feature not to be backported.
   - src/pybind/mgr/dashboard/module.py: fixed linting issue.