Refactor config package

[torives]

📚 Context

While writing our end-to-end tests, it became clear that the current config package wasn't appropriate for the new context, as it is highly cumbersome and error-prone setting/unsetting environment variables for individual tests.

Although #309 made strides in improving the situation by creating a NodeConfig struct, it soon became clear that the whole package would have to be adapted to this new way of handling the node's configuration.