mgr/dashboard: add prometheus read permission to cluster_mgr role

Fixes: https://tracker.ceph.com/issues/70768
Signed-off-by: Nizamudeen A <nia@redhat.com>

Author: nizamial09

src/pybind/mgr/dashboard/services/access_control.py

@@ -257,6 +257,7 @@ def map_to_system_roles(cls, roles: List[str]) -> List['Role']:
         Scope.CONFIG_OPT: [_P.READ, _P.CREATE, _P.UPDATE, _P.DELETE],
         Scope.LOG: [_P.READ, _P.CREATE, _P.UPDATE, _P.DELETE],
         Scope.GRAFANA: [_P.READ],
+        Scope.PROMETHEUS: [_P.READ]
     })