sources/oauth: add WeChat type (#18086)

* Add wechat.

* Refactor comments and formatting in wechat.py

Signed-off-by: Anduin Xue <anduin@aiursoft.com>

* Fix lint.

Signed-off-by: Anduin Xue <anduin@aiursoft.com>

* Fix lint.

* fix: Rename `WeChat` enum member to `Wechat` for consistency

* docs: Add WeChat social login integration guide.

* Docs updates

* Revise WeChat integration instructions

Updated instructions for creating a WeChat Website Application and added details about scopes and user attribute mappings.

Signed-off-by: Anduin Xue <anduin@aiursoft.com>

* Prettier

* Update wechat.py

Signed-off-by: Anduin Xue <anduin@aiursoft.com>

---------

Signed-off-by: Anduin Xue <anduin@aiursoft.com>
Co-authored-by: dewi-tik <dewi@goauthentik.io>
Co-authored-by: Marc 'risson' Schmitt <marc.schmitt@risson.space>

blueprints/schema.json

@@ -11982,7 +11982,8 @@
                         "reddit",
                         "slack",
                         "twitch",
-                        "twitter"
+                        "twitter",
+                        "wechat"
                     ],
                     "title": "Provider type"
                 },