I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[x] Feature request
[x] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

As of now, I can either register the angular-generated service worker (i.e. /ngsw-worker.js) or register my own custom service worker (see documentation: https://angular.io/api/service-worker/ServiceWorkerModule#static-members)

Expected behavior

One should be able to add custom behavior to angular-generated service workers (i.e. /ngsw-worker.js). For instance what if I want to add business logic to the service worker. It would be nice to provide extension points in order to achieve this and document them.

EDIT (gkalpak): Other related issues/issues that could be fixed by this: #24387, #26413, #30195, #46984