FEAT: Simple OAuth2 system

[ChengjieLi28]

Fixes #698

Detail

1. add --auth-config option for xinference-local and xinference-supervisor command for startup xinference with auth system.
2. Nothing changed when using xinference without auth.
3. For web users:
   Firstly, a login web page for sign in when the user tries to open the web UI. Then use the web as before. If user does not have the right permission, UI would show error.
4. For command line users, user should login first:

xinference login --username <name> --password <pass>

Then use the command as before.

5. For SDK users, also login first:

from xinference.client import Client
client = Client('<endpoint>')
client.login('<name>', '<pass>')

[codingl2k1]

LGTM