plug-ins: more debugging data in file-darktable.
darktable GUI is "mangled" when opened from GIMP for a reporter. There was already some debug info outputted (when running with DARKTABLE_DEBUG environment variable). Adding the environment list (and some separation titles to make it easier to distinguish what is what). Hopefully it will help debugging. See #6195 and https://github.com/darktable-org/darktable/issues/7402