Add Service Worker support

[jordanaustin]

Hi there 👋! Just curious about your thoughts of adding service worker support? Is this something you're interested in? I'm happy to help, just want to make sure this aligns with your goals

[thepassle]

I think it would be good to add, but I think it should be in the form of a generator in this repo: https://github.com/open-wc/open-wc

Would love to have a PR for this :-)