Move AvalancheGo install script to the AvalancheGo Repo

[richardpringle]

Context and scope The AvaGo install script is actually useful for any VM, so we should move the script to the AvalancheGo repo then fetch and install from there.

Discussion and alternatives This is an easy change that should be merged in both repos within a day, but the better change would be to turn the install script into a GitHub-Action such that it is usable by any other GitHub-Actions (think 3rd party VM authors).

Open questions None right now...