scripts: use WpConf API to get configuration values

This patch also moves nested configuration objects that are not considered
settings from the wireplumber.settings section to its own configuration
section (eg the rules array, the spa plugin properties, etc...). This allows
those objects to be merged with other same sections defined in other files.

src/scripts/lib/common-utils.lua

@@ -51,7 +51,7 @@ cutils.default_metadata_om = ObjectManager {
 }
 
 function cutils.evaluateRulesApplyProperties (properties, name)
-  local matched, mprops = Settings.apply_rule (name, properties)
+  local matched, mprops = Conf.apply_rules (name, properties)
 
   if (matched and mprops) then
     for k, v in pairs (mprops) do