feat: add a new system metadata service

Signed-off-by: aramissennyeydd <aramis.sennyey@doordash.com>

packages/backend-plugin-api/src/alpha/index.ts

@@ -23,3 +23,16 @@ export type {
 export type { ActionsService, ActionsServiceAction } from './ActionsService';
 
 export { actionsRegistryServiceRef, actionsServiceRef } from './refs';
+
+import { createServiceRef } from '@backstage/backend-plugin-api';
+
+export const systemMetadataServiceRef = createServiceRef<
+  import('./services/definitions/SystemMetadataService').SystemMetadataService
+>({
+  id: 'core.systemMetadata',
+});
+
+export type {
+  BackstageInstance,
+  SystemMetadataService,
+} from './services/definitions/SystemMetadataService';

packages/backend-plugin-api/src/services/definitions/SystemMetadataService.ts

@@ -0,0 +1,25 @@
+/*
+ * 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.
+ */
+
+type Target = string | { internal: string; external: string };
+
+export interface BackstageInstance {
+  url: Target;
+}
+
+export interface SystemMetadataService {
+  listInstances(): Promise<BackstageInstance[]>;
+}