Add embedded GTK UI lib as a dependency of the updater

When building the updater target from outside the updater-installer/
build dir in the context of a larger project, CMake failed
to determine how to build libupdatergtk.so in the context
of the dependency chain updater -> updatershared -> libupdatergtk.cpp ->
libupdatergtk.so

Resolve this for now by adding an explicit updatershared ->
resource_updatergtk dependency.

MD-19678 #time 2h