feat(events/http): add HTTP endpoint-based event publisher

This plugin adds an event publisher which receives events via (an) HTTP endpoint(s)
and can be used as destination at webhook subscriptions.

Relates-to: #11082
Signed-off-by: Patrick Jungermann <Patrick.Jungermann@gmail.com>

plugins/events-backend/config.d.ts

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2022 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.
+ */
+
+export interface Config {
+  events?: {
+    http?: {
+      /**
+       * Topics for which a route has to be registered
+       * at which we can receive events via HTTP POST requests
+       * (i.e. received from webhooks).
+       */
+      topics?: string[];
+    };
+  };
+}