Add an init method in AppController to initialize the app

[LoicPoullain]

Issue

In many situations, we need to make some initialization when starting the server (for example establishing a connection to another server).

For now, we can do it src/index.ts but it is not very handy to access the app services using DI.

const app = createApp(AppController);
app.foal.services.get(MyServiceA).doSomething();
app.foal.services.get(MyServiceB).doAnotherSomething();

Related issue

#516

[LoicPoullain]

Possible Solution

Add an optional init method in the AppController that will be called after the services and controllers have been instantiated.

export class AppController {
  @dependency a: MyServiceA;
  @dependency b: MyServiceB;

  init() {
   this.a.doSomething();
   this.b.doAnotherThing();
  }
}

For backward compatibility on version 1 (people might have already a method named init here), the feature would be disabled by default and should be enabled using a configuration key in config/.

[LoicPoullain]

Feature added in v1.2.0