support NewUserConn operation

* feat: include RunId in FRP Server Plugin NewProxy message

* doc: rewrite server plugin documentation

* refactoring monitor code, support prometheus
* remove vendor

token is the current token comparison, and oidc generates oidc token using client-credentials flow. in addition - add ping verification using the same method

The ServerCommonConf is now passed around as an argument instead of
being shared between components as a global variable. This allows for
more natural interaction with server.Session as a library and allows for
multiple servers to co-exist within the same process.

Related: #1387