* Docs: rename modelstudio.md to qwen_modelstudio.md, add Standard API endpoints
* refine docs
* Docs: fix broken link in providers/index.md after modelstudio rename
* Docs: add redirect from /providers/modelstudio to /providers/qwen_modelstudio
* Docs: adjust the order in index.md
* docs: rename modelstudio to qwen_modelstudio, add Standard API endpoints (#54407) (thanks @wenmengzhou)
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Co-authored-by: George Zhang <georgezhangtj97@gmail.com>