Ensure log_dir points to RUN_PATH from .env file

[chaitjo]

This PR makes a very small change, though I thought its worth opening a PR anyway in order to discuss before merging.

• There’s an unexpected behaviour with our .env file and logging directory. We ask users to provide a RUN_DIR, which assumes that logs and wandb output will be saved there. However, it seems that the RUN_DIR path is never used in the codebase.
• What happens instead is that all logs/wandb outputs/etc. are saved to the log_dir variable in the default hydra config for the environment, which always saves things to a /logs folder within the project’s root directory.
• This PR fixes the above issue.

[amorehead]

LGTM. What say you, @a-r-j?

[a-r-j]

LGTM, thanks @chaitjo !