chore: re-add max listeners (#6522)

## About the changes
Some tests are reporting this error:

`MaxListenersExceededWarning: Possible EventEmitter memory leak
detected. 11 UPDATE_REVISION listeners added to
[ConfigurationRevisionService]. Use emitter.setMaxListeners() to
increase limit`

I thought it's because of this change
https://github.com/Unleash/unleash/pull/6400#discussion_r1511494201 but
it was not.

I've managed to get a trace of the issue following this
https://stackoverflow.com/q/62897235/239613 and now we can identify
`ConfigurationRevisionService` as one explanation. The reason is that
it's a singleton that should be cleaned up after tests.

E.g.:
https://github.com/Unleash/unleash/actions/runs/8248332132/job/22558419656?pr=6517#step:8:15

package.json

@@ -45,7 +45,7 @@
     "prebuild:watch": "yarn run clean",
     "build:watch": "tsc -w --strictNullChecks false",
     "prebuild": "yarn run clean",
-    "test": "NODE_ENV=test PORT=4243 jest",
+    "test": "NODE_ENV=test PORT=4243 node --trace-warnings node_modules/.bin/jest",
     "test:unit": "NODE_ENV=test PORT=4243 jest --testPathIgnorePatterns=src/test/e2e --testPathIgnorePatterns=dist",
     "test:docker": "./scripts/docker-postgres.sh",
     "test:report": "NODE_ENV=test PORT=4243 jest --reporters=\"default\" --reporters=\"jest-junit\"",

src/lib/features/feature-toggle/configuration-revision-service.ts

@@ -78,4 +78,8 @@ export default class ConfigurationRevisionService extends EventEmitter {
 
         return this.revisionId;
     }
+
+    destroy(): void {
+        ConfigurationRevisionService.instance?.removeAllListeners();
+    }
 }

src/lib/middleware/response-time-metrics.test.ts

@@ -52,6 +52,9 @@ describe('responseTimeMetrics old behavior', () => {
         getAppCountSnapshot: jest.fn(),
     };
     const eventBus = new EventEmitter();
+    afterEach(() => {
+        eventBus.removeAllListeners();
+    });
 
     test('uses baseUrl and route path to report metrics', async () => {
         let timeInfo: any;