Consider matching executable names case-insensitively

[autarch]

This was inspired by the https://github.com/bscan/PerlNavigator project, where the releases contain an executable named perlnavigator. I started working on this in a branch named case-insensitive, but it got a bit convoluted.

The main issue is that right now, ubi actually renames files it downloads if they're not in an archive (tar/zip) file. For example, the rust-analyzer-x86_64-unknown-linux-musl.gz file gets installed as rust-analyzer.

Combining this with the case-insensitive matching got a little confusing. I will maybe come back to this in the future.