Folder API: optionally force deleting Grafana 8 alerts when deleting a folder (or error) (#36427) (#37094)

* Folder API: Add an optional query parameter for allowing deleting a  folder containing rules

* Update frontend

- Set forceDeleteRules=true when frontend deletes a folder
- Improve modal text

* Update docs

* Apply suggestions from code review

Co-authored-by: gotjosh <josue@grafana.com>
Co-authored-by: Nathan Rodman <nathanrodman@gmail.com>
Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>
(cherry picked from commit b96dd1877c)

Co-authored-by: Sofia Papagiannaki <papagian@users.noreply.github.com>

pkg/api/folder.go

@@ -96,7 +96,7 @@ func (hs *HTTPServer) DeleteFolder(c *models.ReqContext) response.Response { //
 		return ToFolderErrorResponse(err)
 	}
 
-	f, err := s.DeleteFolder(c.Params(":uid"))
+	f, err := s.DeleteFolder(c.Params(":uid"), c.QueryBool("forceDeleteRules"))
 	if err != nil {
 		return ToFolderErrorResponse(err)
 	}
@@ -149,7 +149,8 @@ func ToFolderErrorResponse(err error) response.Response {
 	if errors.Is(err, models.ErrFolderTitleEmpty) ||
 		errors.Is(err, models.ErrDashboardTypeMismatch) ||
 		errors.Is(err, models.ErrDashboardInvalidUid) ||
-		errors.Is(err, models.ErrDashboardUidTooLong) {
+		errors.Is(err, models.ErrDashboardUidTooLong) ||
+		errors.Is(err, models.ErrFolderContainsAlertRules) {
 		return response.Error(400, err.Error(), nil)
 	}