* If a base path is provided at build time, use it.
* Base path can be set with `VIKUNJA_FRONTEND_BASE` at
build time
* `VIKUNJA_FRONTEND_BASE` sets `import.meta.env.BASE_URL` after Vite resolves it.
* Usages of `import.meta.env.BASE_URL` are statically replaced
at build time.
* If base path is not provided, `import.meta.env.BASE_URL`
defaults to '/'.
* Documentation:
https://vitejs.dev/guide/env-and-mode.html
* Fixes:
* Manifest not loading because of incorrect path.
* Service Worker not loading because path is incorrect in
manifest.
* Service Worker crashing because import of workbox is from
wrong path.
* Service Worker not loading a task because path is incorrect
in event listener.
* Incorrect URLs being set on window because base path is
incorrect.
* ex: `/login` vs `/base/login`
Signed-off-by: Jef Oliver <jef@eljef.me>