Please add OAuth provider for wechat

[jet10000]

https://wechat-oauth2.readthedocs.io/en/latest/index.html

[frankie567]

Hello @jet10000 👋

Why not! OAuth providers implementations are provided by httpx-oauth, and it's quite easy to add a new one (you can draw inspiration from the Discord one, for example). I would be happy to review a PR and then enable it in Fief.