feat(core): Add app.teardown functionality

[idaho]

This feature is about to shut down the application and run teardown functionalities after the http server is closed on each service.

In some cases, e.g. when we stop/restart the Node application, the connections to various databases are not closed properly and remain open until the system closes these open connections after some time.

As a counterpart to app.listen() there is now the method app.close() which closes the http server and then calls the teardown methods of the individual services.

In this way, logic for teardown can also be implemented as in the setup methods of the services.

import app from './app';

const server = await app.listen(1234);

const close = async (): Promise<void> => {
  await app.close();
  process.exit(1);
};

process.on('SIGINT', close);
process.on('SIGTERM', close);

As I even saw in PR #2510, it would even be a good idea to implement an addTeardown method where we can configure the logic to happen at the application level.