Generally it seems user agents are all `software/version` but ours is
not. Also, set the user agent in a way that it's shared between Bash
and Ruby code.
Closes https://github.com/Homebrew/legacy-homebrew/pull/50480.
This is the (partially) documented public API for Homebrew.
The main class you should look at is the {Formula} class (and classes linked from there). That's the class that's used to create Homebrew formulae (i.e. package descriptions). Assume anything else you stumble upon is private.