Chore: move environment-specific code to its own package(s) #45
Description
The main goal of this is to separate out the main distributed learning functions of distrib-rl from the environment-specific initialization logic that is currently found in the distrib_rl/Environments/Custom directory.
To do this we should move the RocketLeague env to its own repo (likely in the nexus-rl org), and move the other two envs into their own packages that live alongside the distrib_rl package directory in this repo.