Alerting: handle folder permissions when fine-grained access enabled (#47035)

* Use alert:create action for folder search with edit permissions. This matches the action that is used to query dashboards (the update will be addressed later)
* Update rule store to use FindDashboards instead of folder service to list folders the user has access to view alerts. Folder service does not support query type and additional filters. 
* Do not check whether the user can save to folder if FGAC is enabled because it is checked on API level.

pkg/services/ngalert/api/api_prometheus.go

@@ -85,7 +85,7 @@ func (srv PrometheusSrv) RouteGetRuleStatuses(c *models.ReqContext) response.Res
 		labelOptions = append(labelOptions, ngmodels.WithoutInternalLabels())
 	}
 
-	namespaceMap, err := srv.store.GetNamespaces(c.Req.Context(), c.OrgId, c.SignedInUser)
+	namespaceMap, err := srv.store.GetUserVisibleNamespaces(c.Req.Context(), c.OrgId, c.SignedInUser)
 	if err != nil {
 		return ErrResp(http.StatusInternalServerError, err, "failed to get namespaces visible to the user")
 	}