* Make authentication part of the server, so it can be reused outside the Native API
This commit has broken tests after a rebase
* Serve frontend assets from `server`, and not from Native API
* Change Native API URL
* Fix auth tests
* Refactor server authentication
* Simplify authProvider, now subsonic token+salt comes from the server
* Don't send JWT token to UI when authenticated via Request Header
* Enable ReverseProxyWhitelist to be read from environment
See https://pkg.go.dev/github.com/robfig/cron#hdr-CRON_Expression_Format for expression syntax.
`ScanInterval` will still work for the time being. The only situation it does not work is when you want to disable periodic scanning by setting `ScanInterval=0`. If you want to disable it, please set `ScanSchedule=""`
Closes#1085
