Add "Latest" To Docsite Learn Versioning

Derived from: https://github.com/DioxusLabs/docsite/issues/436

The `latest` tag should be used in addition to version number. Currently the learn link uses the latest version number https://dioxuslabs.com/learn/0.6 . Using `latest` would allow users to create bookmarks to the current docs. For search engines, like google, they don't really understand that versions like `0.5` are obsolete until more users start using the `0.6` docs and enough time has past. Therefore a lot of google searches for questions lead to old documentation like `0.5` or `0.4`. If something like `latest` was also used, overtime as these pages are used more frequently, they will be served more.

Though, as outlined in the linked issue

> We have also added noindex to the old documentation to remove it from search results, but that takes some time to apply

This may be mitigated going forward. But even with `noindex` the engine has to re-learn/re-rank each new version page is what the user is looking for (based on search traffic).