Add an installer-less, distribution-agnostic, low-privilege Linux build of Positron

[jmcphers]

Today, we currently have two Positron release binaries for Linux, a .deb installer and an .rpm installer. This covers most Linux distributions, but not all, and it makes it difficult to use Positron on Linux if you don't have admin rights.

We should add a Linux release binary that is a regular .tar.gz file that can be used on any Linux distribution (that otherwise meets glibc and openssl requirements) and doesn't require admin privileges, just as e.g. VSCodium has.

https://github.com/VSCodium/vscodium/releases