core: Replace legacy INI config system with Pydantic-based TOML configuration.

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.

libervia/backend/plugins/plugin_misc_app_manager/__init__.py

@@ -30,6 +30,7 @@ from twisted.internet import defer
 from twisted.python.procutils import which
 from yaml.constructor import ConstructorError
 
+from libervia.backend import G
 from libervia.backend.core import exceptions
 from libervia.backend.core.constants import Const as C
 from libervia.backend.core.i18n import _
@@ -177,7 +178,7 @@ class AppManager:
                 "is expected"
             )
 
-        value = self.host.memory.config_get(section, name, default)
+        value = getattr(getattr(G.config, section), name) or default
         # FIXME: "public_url" is used only here and doesn't take multi-sites into account
         if name == "public_url" and (not value or value.startswith("http")):
             if not value: