Better app settings management

[mpangrazzi]

With this, I am adding a better app settings management using pydantic-settings and dotenv files.

Now all app settings are centralised in settings.py and they can be provided both as env variables, hayhooks run command args or they can simply be in a .env file (in the same folder where you run hayhooks).

I've also refactored all os.environ usages around the app.

Note: after this, I will add open-webui support as a feature flag.

Extra: I've added an .editorconfig file for better consistency across editors.

[vblagoje]

Looks good!