fix: DeleteMultipleObjects to finish even if cancelled + concurrent sets (#14038)

* Process sets concurrently.
* Disconnect context from request.
* Insert context cancellation checks.
* errFileNotFound and errFileVersionNotFound are ok, unless creating delete markers.

cmd/bucket-handlers.go

@@ -576,6 +576,9 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 		return
 	}
 
+	// Disable timeouts and cancellation
+	ctx = bgContext(ctx)
+
 	deleteList := toNames(objectsToDelete)
 	dObjects, errs := deleteObjectsFn(ctx, bucket, deleteList, ObjectOptions{
 		Versioned:        versioned,