Revert "Separate port for prometheus metrics"

This reverts commit 58f5b6806e.

src/lib/Server.js

@@ -388,6 +388,11 @@ module.exports = class Server {
     if (ENABLE_PROMETHEUS_METRICS === 'true') {
       const appMetrics = createApp();
       this.app_metrics = appMetrics;
+      appMetrics.use(fromNodeMiddleware(expressSession({
+        secret: crypto.randomBytes(256).toString('hex'),
+        resave: true,
+        saveUninitialized: true,
+      })));
       const metricsRouter = createRouter();
       appMetrics.use(metricsRouter);
       metricsRouter