Support old links on extensions docs

[aalves08]

Is your feature request related to a problem? Please describe.

With the new versioned extensions docs, old links like https://extensions.rancher.io/extensions/extensions-getting-started won't work because they don't include the version param like next or v2

https://extensions.rancher.io/extensions/next/extensions-getting-started
https://extensions.rancher.io/extensions/v2/extensions-getting-started

A redirect solution was implemented, but it's not working properly: https://docusaurus.io/docs/api/plugins/@docusaurus/plugin-client-redirects -> implemented with PR #12491

Describe the solution you'd like

Redirect old links to next (v3) version of docs

Describe alternatives you've considered

Additional context

[gaktive]

@aalves08 this can be independent of the January releases so I'll move this to 2.11.0 with the assumption it can be done at any time. Let me know if we need to do anything immediately though.