feat: httpadmin protocol for external control

[vforvideo]

idea

clash-core has external control that support restful api for external control. That makes it easy for third part GUI to manipulate it. So I think it's a good idea for python proxy.

This pr is draft for this idea. I'd like to hear your suggestions about it. :)

usage

Add a new protocol called httpadmin, which handle http request. So user can add admin port:

% pproxy -l http://localhost:8080 -l httpadmin://localhost:8081

At beginning stage, two api entries are added.

Show server status

% curl 'localhost:8081/status'

Show server configs (list argv)

% curl 'localhost:8081/configs'

Modify server configs (use new argv)

% curl 'localhost:8081/configs' -X POST -d '-l http://localhost:8082 -l httpadmin://localhost:8081'

known issues (todo)

• it's dangerous to expose admin port, auth is necessary
• hot reload uses raise KeyInterrupt, maybe there's more elegant way