This avoids hearing mono audio only on the left speaker

the _can_link function was previously assuming that the target
stream is always specified in the configuration file

So that we can use media.role to specify the stream

Big API break happens after this commit and we cannot
keep up right now.

The role defined in the endpoint-link configuration files must have higher
priority than the one set in the endpoint. If none of them are set, the config
policy fallbacks to the lowest one defined in the streams configuration file

Currently all it does is that it prints the properties
of all device nodes (Audio/Source & Audio/Sink), which
is useful for editing the configuration files

Otherwise, if the object manager is destroyed while a sync is in progress,
we get an invalid 'self' pointer on the callback later, which is being
called regardless

There is a bit more work that should be done in the core to avoid leaking
this ref in case pipewire disconnects before the sync is completed

This will be replaced by a new policy based on configuration files

The purpose of this change is to have a generic API that allows modules to read
configuration data from files under a specific directory. Since we can have many
types of configuration files, this new class maps file extensions with generic
parsers defined in the modules, giving modules full freedom to parse any kind of
data.