Clean up configuration format and directory

Currently the debian/config directory contains:

• Global and per-package configuration files, in INI format with very loosely defined schemas
• EULA texts
• Additional (never upstream) and replacement (downgraded) firmware files

It doesn't make much sense to include the additional and replacement firmware here, so move them to a new debian/added-firmware/ directory which is common, not per-package.

Convert the configuration to TOML format, as was done previously in src:linux, and use dataclasses and dacite to parse it with a properly defined schema. Combine all the configuration into a single file, and also include the EULA texts there since TOML supports multi-line strings.

Depends on !144 (merged)