refactor shared.py with a frozen CONFIG dataclass object

[yangm2]

use a frozen dataclass object as a cannonical source of truth rather than mutable environment variables

• consolidate os.getenv() calls to shared.py
  • centralize the resolution of defaults vs execution environment vs .env
• create an immutable object with configuration data
• avoid current-working-directory (i.e. CWD) assumptions for dir/file locations (i.e. DATA_DIR, .env). They will now be relative to the backend directory in the repo

[apkostka]

I appreciate the refactor. I'm currently in the process of refactoring the chat module, and I've done a few things in that branch;

• remove references to feedback / training as they are no longer used (including DATA_DIR)
• move things in the shared module to their respective modules (DEFAULT_INSTRUCTIONS goes in chat.py)

I like what you've done with the config, maybe make a new module called config.py and move that there? I'd like to avoid having a generic shared module. Then this will be easier to merge with mine.

[yangm2]

I'm going to put this on the back-burner until after #121 gets merged.