Installing Gleam, Erlang, and Elixir

[lpil]

It would be useful to have a tool to install these dependencies. The main challenge is where do we get the builds from?

• Gleam can be taken from gleam-lang/gleam
• Elixir can be taken from elixir-lang/elixir
• Erlang
  • Windows can be taken from erlang/otp
  • macOS can be taken from erlef/otp_builds
  • Linux has hexpm/bob, but it's Ubuntu only.

We need something for Linux.

Related: erlef/otp_builds#39