this directory may be used to share files between backend and frontends. Normally, an
os-dependent temporary directory is created for that, but if this option is set, the
directory will be created in <local_dir>/<cache_dir>, which may be useful in some use case
(e.g. containerized frontends and backend).
This is an implementation of the protoXEP that will be submitted to XSF. It handle
establishment of a remote control session, and the management of A/V calls with XEP-0167.
rel 436
the `C.META_TYPE_FILE` can't be used in this case as it is a preflight and we don't have
yet data such as progress ID. `C.META_TYPE_FILE` is used as a sub-type to help with dialog
management in frontend.
default location of pid file is now specific to logged user, this allow to run several
instances of Libervia by different users on the same machine without PID conflicts.
