Alerting: Implement GetStatus in the remote Alertmanager struct (#84887)

* Alerting: Implement GetStatus in the remote Alertmanager struct

* update tests

* fix tests, extract AlertmanagerConfig from PostableConfig

* get the remote AM config instead of the Grafana one from the remote AM

* pass grafana AM config in test

* return error in GetStatus instead of logging it (internal AM)

pkg/services/ngalert/api/api_alertmanager.go

@@ -48,7 +48,12 @@ func (srv AlertmanagerSrv) RouteGetAMStatus(c *contextmodel.ReqContext) response
 		return errResp
 	}
 
-	status := am.GetStatus()
+	status, err := am.GetStatus(c.Req.Context())
+	if err != nil {
+		srv.log.Error("Unable to get status for the alertmanager", "error", err)
+		return ErrResp(http.StatusInternalServerError, err, "failed to get status for the Alertmanager")
+	}
+
 	if !c.SignedInUser.HasRole(org.RoleAdmin) {
 		notifier.RemoveAutogenConfigIfExists(status.Config.Route)
 	}