feat(api): add delete speaker functionality and corresponding tests

- Implemented a DELETE endpoint for removing speakers, including necessary authorization checks and response handling.
- Added a handler for the delete operation in the HTTP API.
- Created unit tests to verify the delete functionality, ensuring proper deletion and response codes.
- Updated OpenAPI documentation to reflect the new delete speaker endpoint.

docs/openapi.yaml

@@ -2379,6 +2379,21 @@ paths:
           $ref: "#/components/responses/NotFound"
         default:
           $ref: "#/components/responses/DefaultProblem"
+    delete:
+      tags: [Speakers]
+      summary: Удалить спикер
+      description: >
+        Удаляет BGP-спикер. Пиры с `bgp_speaker_id` этого спикера остаются, привязка сбрасывается (ON DELETE SET NULL).
+      operationId: deleteSpeaker
+      parameters:
+        - $ref: "#/components/parameters/IdempotencyKey"
+      responses:
+        "204":
+          description: Удалено.
+        "404":
+          $ref: "#/components/responses/NotFound"
+        default:
+          $ref: "#/components/responses/DefaultProblem"
 
   /v1/revisions:
     get: