Fix graceful shutdown

[timja]

Jira link

Follow up to a bug introduced in https://tools.hmcts.net/jira/browse/DTSPO-17277

Change description

Previously this was completely broken, it only worked on the https server which is only used locally.
It also only stopped new requests after 4 seconds and then began closing them.

Shuts the server down so that new connections are no longer accepted by the server.
A hard shutdown of the server happens at 10 seconds now.

Testing done

I implemented a route with a delay of 10 seconds and then 20 seconds before it responds.

+  app.get('/random10', (req, res) => {
+    setTimeout(() => {
+    res.render('home');
+  }, 10000)
+  });
+  app.get('/random20', (req, res) => {
+    setTimeout(() => {
+    res.render('home');
+  }, 20000)
+  });

The 10 second route shutdown cleanly with a 10 second delay roughly:

^C2024-09-10T14:53:35+01:00 - info: [server] ⚠️ Caught SIGINT, gracefully shutting down
2024-09-10T14:53:44+01:00 - info: [server] Connections closed, exiting

The 20 second route was forcefully shutdown:

^C2024-09-10T14:53:58+01:00 - info: [server] ⚠️ Caught SIGINT, gracefully shutting down
2024-09-10T14:54:08+01:00 - info: [server] Forcesfully shutting down application

With no open connections it shuts down immediately:

^C2024-09-10T15:03:52+01:00 - info: [server] ⚠️ Caught SIGINT, gracefully shutting down
2024-09-10T15:03:52+01:00 - info: [server] Connections closed, exiting

I reverted the healthcheck changes as when no more connections are allowed it never responded anyway:

curl localhost:3100/health/readiness
curl: (7) Failed to connect to localhost port 3100 after 0 ms: Couldn't connect to server

Checklist

• commit messages are meaningful and follow good commit message guidelines
• README and other documentation has been updated / added (if needed)
• tests have been updated / new tests has been added (if needed)
• Does this PR introduce a breaking change