This is a huge configuration refactoring.
The configuration system now uses Pydantic settings, with better validation, better
support for environment variables and other goodies.
The main config files now use TOML instead of INI, this allow for better handling of
complex types, notably dict.
Plugins, components and frontends can declare their config settings in a class which will
be imported dynamically.
- MbData is now a Pydantic based model.
- Bridge method has been updated to use `service` and `node` from MbData instead of using
separate fields.
- Added `In-Reply-To` to MbData.
- Adapted code using XEP-0277 to work with the changes.
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