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>

docs/sources/http_api/folder.md

@@ -237,7 +237,9 @@ Content-Length: 97
 
 `DELETE /api/folders/:uid`
 
-Deletes an existing folder identified by uid together with all dashboards stored in the folder, if any. This operation cannot be reverted.
+Deletes an existing folder identified by UID along with all dashboards (and their alerts) stored in the folder. This operation cannot be reverted.
+
+If [Grafana 8 Alerts]({{< relref "../alerting/unified-alerting/_index.md" >}}) are enabled, you can set an optional query parameter `forceDeleteRules=false` so that requests will fail with 400 (Bad Request) error if the folder contains any Grafana 8 Alerts. However, if this parameter is set to `true` then it will delete any Grafana 8 Alerts under this folder.
 
 **Example Request**:
 
@@ -265,6 +267,7 @@ Status Codes:
 
 - **200** – Deleted
 - **401** – Unauthorized
+- **400** – Bad Request
 - **403** – Access Denied
 - **404** – Folder not found