This allows loading objects on demand by adding entries on the
"sm-objects" metadata object.
It is useful to dynamically load pipewire modules such as loopbacks
or network modules without having to start a new pipewire process with
a hardcoded config file.
It is also useful to load new metadata objects in order to implement
the singleton metatada concept as discussed in pipewire!1742
This may be expanded in the future to be able to load other types of
objects.
The key name, combined with the subject, is considered a unique id for
this instance of the object. The value should be a json object with
a 'type' specifying the type of object, together with a 'name' and 'args'
