Changes:
- Overhauled the use of API endpoints. They are now stored in localStorage
- In the settings page, you can now opt in or out of the legacy API (using /api/v1/machine instead of the new /api/v1/node)
- Until headscale 0.23 is released, legacy API will be on by default.
- Caddyfile and Dockerfile now use PORT environment variable (and build argument) so the port on which headscale-admin is served can be changed