Alerting: Refactor API endpoints for fetching alert rules (#37055)

* Refactor ruler API endpoint for listing rules

* Refactor prometheus API endpoint for listing rules

* Update HTTP API docs

pkg/services/ngalert/api/api_prometheus.go

@@ -2,7 +2,6 @@ package api
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
 	"time"
@@ -62,8 +61,19 @@ func (srv PrometheusSrv) RouteGetRuleStatuses(c *models.ReqContext) response.Res
 		},
 	}
 
+	namespaceMap, err := srv.store.GetNamespaces(c.OrgId, c.SignedInUser)
+	if err != nil {
+		return ErrResp(http.StatusInternalServerError, err, "failed to get namespaces visible to the user")
+	}
+
+	namespaceUIDs := make([]string, len(namespaceMap))
+	for k := range namespaceMap {
+		namespaceUIDs = append(namespaceUIDs, k)
+	}
+
 	ruleGroupQuery := ngmodels.ListOrgRuleGroupsQuery{
-		OrgID: c.SignedInUser.OrgId,
+		OrgID:         c.SignedInUser.OrgId,
+		NamespaceUIDs: namespaceUIDs,
 	}
 	if err := srv.store.GetOrgRuleGroups(&ruleGroupQuery); err != nil {
 		ruleResponse.DiscoveryBase.Status = "error"
@@ -77,13 +87,6 @@ func (srv PrometheusSrv) RouteGetRuleStatuses(c *models.ReqContext) response.Res
 			continue
 		}
 		groupId, namespaceUID, namespace := r[0], r[1], r[2]
-		if _, err := srv.store.GetNamespaceByUID(namespaceUID, c.SignedInUser.OrgId, c.SignedInUser); err != nil {
-			if errors.Is(err, models.ErrFolderAccessDenied) {
-				// do not include it in the response
-				continue
-			}
-			return toNamespaceErrorResponse(err)
-		}
 		alertRuleQuery := ngmodels.ListRuleGroupAlertRulesQuery{OrgID: c.SignedInUser.OrgId, NamespaceUID: namespaceUID, RuleGroup: groupId}
 		if err := srv.store.GetRuleGroupAlertRules(&alertRuleQuery); err != nil {
 			ruleResponse.DiscoveryBase.Status = "error"