Move more setup from Bash to Rust

[fitztrev]

Bash script will now compile the binary and then the host will run the binary directly, instead of running cargo run via Docker like it did before.

The Rust code is now responsible for creating the repo dirs and cloning.

Goal is to cleanup the bash script and try to limit it to being just a wrapper around various docker commands.

This branch on gitpod: https://gitpod.io/#https://github.com/lichess-org/lila-docker/tree/rust

[trevorbayless]

Great changes and working perfectly! I'd recommend using if command -v rustup &> /dev/null instead of which though. Not only will it remove the extra output that's generated when rustup is missing, but it's also safer. Here's a good write up on it: https://stackoverflow.com/a/677212/4433744