feat(integrations): add mock integration (#3505)

packages/integrations/src/interfaces/indexer-manager/indexer-manager-integration.ts

@@ -0,0 +1,6 @@
+import type { Indexer } from "./indexer-manager-types";
+
+export interface IIndexerManagerIntegration {
+  getIndexersAsync(): Promise<Indexer[]>;
+  testAllAsync(): Promise<void>;
+}