Old texlive packages download from slow mirror (we should first try ftp)

[hattom]

Closely related to #17871, but I split them up for simplicity.

I switched from the ftp path to an https path, since at least @boegel said that ftp was an issue where he is and for others.

But the https path is a mega-slow mirror (and I read somewhere that we should also try to avoid hammering that host), almost unusably so.
So my suggestion is to do:
try ftp || try https

Logically this isn't so hard to do, but I document this here so we can merge up the open PRs like #17893 (and probably close #17871) to get something working and tackle slowness later.