Generic branch aliases (beyond the built-in "latest")

[itamarst]

We have a release tag and a release branch, and we'd like to continue pushing documentation improvements to the release branch so documentation gets updated without having to do a release.
Given RTD's use of branch names in the URL/version listing, however, we need to name the release branch in a way that looks OK as part of a URL, which is a bit silly.

It would be nice if branches could be configured with aliases, so we could say something like "branch release/myproject-0.1 should display as 0.1".

[ericholscher]

👍 on adding an alias concept. The names of VCS tags & branches aren't always meant to be user facing. We should add the ability to add a specific alias to each Version, which would then be it's user facing slug.

[agjohnson]

Moving this to #4001, where we discuss adding more version aliasing rules.