Document generated sw.ts content

[OlliTietavainenVaadin]

Hilla apps generate a default sw.ts file in the target folder. If a PWA application wants to add additional service worker functionality, the generated content must be taken into account or the application will break. The framework-required functionality should be documented so that a customized sw.ts can take that into account. Any further changes in the generated service workers should also be mentioned in release notes so that developers who customize service workers can adapt to said changes.