examples: add PWA w/ Dioxus CLI template

[arqalite]

This closes #414.

I added a PWA template that uses Dioxus CLI, with a functioning service worker and manifest. The PWA supports cache, is installable and works offline (provided that the user adds the project files in the service worker JS file when creating their project).

[ealmloff]

Thank You! This mostly looks good, just a few issues getting it to integrate with CI correctly. Because this is a full package example, I think we need to add it to the workspace here so that the CI will compile and lint it