Alerting: Improve error when receiver or time interval used by rule is deleted (#86865)

* Alerting: Improve error when receiver used by rule is deleted

* Remove RuleUID from public error and data

* Improve fallback error in am config post

* Refactor to expand to time intervals

* Fix message on unchecked errors to be same as before

pkg/services/ngalert/api/api_alertmanager.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/go-openapi/strfmt"
+
 	alertingNotify "github.com/grafana/alerting/notify"
 
 	"github.com/grafana/grafana/pkg/api/response"
@@ -304,7 +305,7 @@ func (srv AlertmanagerSrv) RoutePostAlertingConfig(c *contextmodel.ReqContext, b
 		return response.Error(http.StatusConflict, err.Error(), err)
 	}
 
-	return ErrResp(http.StatusInternalServerError, err, "")
+	return response.ErrOrFallback(http.StatusInternalServerError, err.Error(), err)
 }
 
 func (srv AlertmanagerSrv) RouteGetReceivers(c *contextmodel.ReqContext) response.Response {