feat(notifications): support notification send throttling

Signed-off-by: Hellgren Heikki <heikki.hellgren@op.fi>

plugins/notifications-backend/config.d.ts

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2024 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import { HumanDuration } from '@backstage/types';
+
+export interface Config {
+  /**
+   * Configuration options for notifications-backend
+   */
+  notifications?: {
+    /**
+     * Concurrency limit for notification sending, defaults to 10
+     */
+    concurrencyLimit?: number;
+    /**
+     * Throttle duration between notification sending, defaults to 50ms
+     */
+    throttleInterval?: HumanDuration | string;
+  };
+}