Install mise via mstrap, outside of Homebrew, allowing for installation prior to Homebrew

[maxfierke]

This will be important for automating getting Ruby installed & Homebrew setup on linux-arm64/aarch64. On of the challenges with getting setup on non-darwin arm64/aarch64 target, is that Homebrew does not ship a portable Ruby installation, requiring those platforms to install a compatible Ruby version first.

By installing mise upfront, and using it to install a compatible Ruby version as-needed, we can make the experience much easier for Linux on arm64/aarch64