Draft: config: move commented configuration into their own override file

The override configuration files will be installed under /etc

@gkiagia @ashoks is there a better name for the configuration override file? I named it wireplumber-override.conf for now. Bear in mind that we cannot name the override files the same as base configuration files, this is because users might want to install them in the same directory by configuring meson's datadir and sysconfigdir with the same path.

Finally, there is currently no way to unload a module in wireplumber-override.conf that is loaded in wireplumber.conf. This is because array elements are appended and object properties are merged, so doing wireplumber.components = [] won't do anything (it would append an empty array to the current wireplumber.components array, instead of resetting it). If a user wants to do that, he could copy wireplumber.conf into /etc, and then remove the module that he does not want to load from the array list in that file. I guess this is OK?

Another thing to keep in mind is to never add new settings in wireplumber.conf. Instead, they should always be added in wireplumber-override.conf commented, and wireplumber should always use a default value if the property is not found in WpSettings. Eventually, it would be great to have wireplumber working without any base configuration, and the users would just uncomment settings in the override configuration files to change functionality.