Build service-worker.js to /static to work better with next export

[mfix22]

Since next export automatically copies files from /static into the build folder, if the service-worker.js was output to there, then users wouldn't have to manually copy it over to the public directory (like we do here)

[hanford]

Would love a PR

Feel free to ping me if you have any questions!

[joaovieira]

The sw output should be defined by the swDest option from workbox and everything else should work around it.

Is /static the right place? That's what next-workbox does, but it felt odd to me as well given it's not a generated folder and generating files into user folders may be unexpected. On the other side, .next/static is not automatically exported.

Ideas?

[mfix22]

It was actually working correctly! There was just a bug from using path.join instead of resolve (: PR mentioned above fixes it