docs website support multiple version

[Justinterest]

Purpose

• support docs multiple version
• make API version same with docs version

Changes

• change docs routeBasePath from / to /docs
• add client redirect plugin
• remark plugin for variables and fragment support versions
• add index page for redirecting to docs (fix docs link to / address build error)
• rewrite the docs sync script to support lastest two version sync
• add auto api global data and auto api generate route only lastest two version
• change theme's navbaritem to support switch api version using global version
• remove netlify redirect rules

[netlify]

✅ Deploy Preview for docs-taichi-graphics ready!

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[rexwangcc]

Looked through the preview page, LGTM! Thanks for the heavy-lifting work!