Alerting: Support for optimistic locking for alert rules (#50274)

* add support for optimistic locking for alert_rule table
* return 409 in the case of opitimistic lock

pkg/services/ngalert/api/api_ruler.go

@@ -467,6 +467,8 @@ func (srv RulerSrv) updateAlertRulesInGroup(c *models.ReqContext, groupKey ngmod
 			return ErrResp(http.StatusForbidden, err, "")
 		} else if errors.Is(err, ErrAuthorization) {
 			return ErrResp(http.StatusUnauthorized, err, "")
+		} else if errors.Is(err, store.ErrOptimisticLock) {
+			return ErrResp(http.StatusConflict, err, "")
 		}
 		return ErrResp(http.StatusInternalServerError, err, "failed to update rule group")
 	}