Configuration file based approach to config

Current we use a python module to provide configuration. The only option to override configuration in different environments is through environment variables. This is cumbersome and limited, since environment variables have no structure or types. It leads to ugly config scripts (e.g. helm charts).

We should refactor to a solution that:

• is based on an external configuration file
• allows partial overrides from other files
• still allows overrides from environment variables