Links without locale & branch are broken

[MichaelDeBoey]

https://reactrouter.com/start/concepts used to redirect to https://reactrouter.com/en/main/start/concepts, but this doesn't seem to work anymore

We use these in several of the Remix docs, so all these links are now broken

[brophdawg11]

We removed this "version-less" redirect because it was prone to breaking across major releases. For example, when we remove json in v7, https://reactrouter.com/fetch/json would have started to 404 because the links will always redirect to the latest version and v7 doesn't have that API. Instead, we need to always include some known good version for these links - so we moved to a format of https://reactrouter.com/v6/fetch/json which will redirect to the latest in the v6 release line.

We need to go fix some of these old types of links - I did a handful for RR in remix-run/react-router#12141 and have some local changes for the Remix repo as well that I'll get pushed shortly and will drop a link here too. If you see others that aren't in the source code please let us know!

[brophdawg11]

Remix PR remix-run/remix#10130