### What problem does this PR solve?
Deprecate `/github_callback` route in favor of
`/oauth/callback/<channel>` for GitHub OAuth integration:
- Added GitHub OAuth support in the authentication module
- Introduced `GithubOAuthClient` with methods to fetch and normalize
user info
- Updated `CLIENT_TYPES` to include GitHub OAuth client
- Deprecated `/github_callback` route and suggested using the generic
`/oauth/callback/<channel>` route
---
- Related pull requests:
- #7379
- #7553
### Usage
- [Create a GitHub OAuth
App](https://github.com/settings/applications/new) to obtain the
`client_id` and `client_secret`, configure the authorization callback
url: `https://your-app.com/v1/user/oauth/callback/github`
- Edit `service_conf.yaml.template`:
```yaml
# ...
oauth:
github:
type: "github"
icon: "github"
display_name: "Github"
client_id: "your_client_id"
client_secret: "your_client_secret"
redirect_uri: "https://your-app.com/v1/user/oauth/callback/github"
# ...
```
### Type of change
- [x] Documentation Update
- [x] Refactoring (non-breaking change)
