* Get rid of ugly statik
go1.16 introduced the embed package, it's the more graceful solution for embedding file into binary.
https://golang.org/pkg/embed/
* remove statik totally
* split go and static files in assets
token is the current token comparison, and oidc generates oidc token using client-credentials flow. in addition - add ping verification using the same method
This option allows users to specify where they want assets to be loaded
from, like the "assets_dir" option that already exists for frps. This
allows library users to use the admin panel without having to bundle
assets with statik.