An easy way to configure redirects

[thanethomson]

I suspect that, at some point soon, we're going to need some kind of simple mechanism to specify redirects.

For instance, we're currently making our v0.37.0 release candidates' docs available via https://docs.cometbft.com/v0.37-rc/, but soon, when we cut v0.37.0, the documentation will be available from the /v0.37/ path and not from the /v0.37-rc/ path any more.

With the old Vuepress-based site, there was a simple REDIRECTS file (similar to the VERSIONS file in this repo) that allowed us to specify:

/old/path/ /new/path/
/old/path/2/ /new/path/2/

Where this would automatically generate index.html files at /old/path/index.html that would redirect to /new/path/.

It'd be great if we could implement the same or a similar mechanism that achieves the same kind of outcome in an easy way. The question of where to store it, however, is still up for debate (i.e. for this particular file, do we store it in the cometbft repo, or in the cometbft-docs repo?).