The `send_email` calls in `send_emails` passed the plugin `EmailSettings` as the `config`
argument, raising `AttributeError` on account creation and leading to the profile
deletion.
They now pass the main config via a new `email_settings`.
`credentials_xmpp_connect` takes a new `send_email` flag to let frontends skip the admin
notification email (notably useful in web local mode).
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.
