Switch from asdf to homebrew

What does this MR do?

This shaves around 40min (37%) from the toolchain build, by not compiling from source asdf plugins such as postgres, ruby, python...

We're also almost guaranteed that brew packages install, compile, and generally work together in a consistent way, compared to integrating asdf plugins with brew dependencies, so this will make maintenance easier.

Since we pin the version of our taps, all brew dependencies are pinned.

Why was this MR needed?

What's the best way to test this MR?

What are the relevant issue numbers?