refactor: config: Overhaul `Config` interface
This MR implements several improvements to the `Config` interface.
- Replace getters with public member variables.
- Detach the `ConfigMap` class handling parsing for the two backends from the main configuration interface and logic.
- Add exception handling for internal data getters and data type conversions.
- Refactor SCONE address elements into its data structure.
- Rename variables to Google C++ style where practical.