Context

Config is currently managed via two files: boaviztapi/data/config.yml, and tests/data/config.yml.

There are a couple of issues with the current setup:

• It's not possible to override config at runtime (e.g. with environment variables)
• The two existing YAML files are almost identical
• The ALLOWED_ORIGINS and SPECIAL_MESSAGE parameters are configurable via environment variables, but is managed inline in main.py here and here
• The doc has a small typo, referencing config.json

Changes

• Allow overriding default config values with environment variables
• Have a single definition of the default config values, and override for tests only where necessary
• Update doc to reflect changes

We could use pydantic-settings to manage the settings, and the pytest-env package could be used to modify environment variables for all tests.

We could also move the configuration of our data directories to this config, as they are currently handled in Python code here.