Add GitCode to the list of supported providers

[gehongyan]

This pull request would like to add GitCode to the list of supported providers.

[gehongyan]

Docs

GitCode offers documentation in Chinese and English for the first and second editions. These versions pertain solely to the documentation and not to the API versions.

• Authorization mechanism in doc v1
• Token API in doc v2

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Hint

• It appears that GitCode does not support setting the scopes through query strings; the configuration of scopes (App permissions) is instead managed within the OAuth app management on the official web.

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Useful Screenshots

Texts in these screenshots are all auto-translated by Google Chrome

• GitCode OAuth App Editing

• Requesting Authentication

• Authenticated (ASP.NET)

• Authenticated (Console)

• Refreshing

[kevinchalet]

Merged. Thanks for this great contribution, @gehongyan! ❤️ 🎉