refactor: apply more review suggestions

Co-authored-by: Fredrik Adelöw <freben@gmail.com>
Co-authored-by: Patrik Oldsberg <poldsberg@gmail.com>
Signed-off-by: Camila Belo <camilaibs@gmail.com>

packages/backend-plugin-api/report.api.md

@@ -509,7 +509,7 @@ export interface RootHttpRouterService {
 // @public
 export interface RootLifecycleService extends LifecycleService {
   // (undocumented)
-  addBeforeShutdownHook(hook: () => void): void;
+  addBeforeShutdownHook(hook: () => void | Promise<void>): void;
 }
 
 // @public

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

@@ -24,5 +24,5 @@ import { LifecycleService } from './LifecycleService';
  * @public
  */
 export interface RootLifecycleService extends LifecycleService {
-  addBeforeShutdownHook(hook: () => void): void;
+  addBeforeShutdownHook(hook: () => void | Promise<void>): void;
 }