Add department_selfserve_path_confirmations table and enhance PingApiTest

Introduce a new database table `department_selfserve_path_confirmations` to store path confirmations related to department configurations. Update `PingApiTest` to verify additional keys, ensuring `backend_version` and `api_commit_sha` are checked in the response.

services/nginx/app/tests/Api/PingApiTest.php

@@ -17,5 +17,7 @@ it('returns the ping contract', function (): void {
     expect($response->data())
         ->toBeArray()
         ->toHaveKey('message', 'pong')
-        ->toHaveKey('time');
+        ->toHaveKey('time')
+        ->toHaveKey('backend_version')
+        ->toHaveKey('api_commit_sha');
 });