recipe: add helper method to allow inherit from a recipe
It is intended for self-contained projects and test.
Example of inherit:
original_recipe = import_recipe('recipes/gst-plugins-rs.recipe')
class Recipe(original_recipe):
def prepare(self):
self.cargo_packages = [
'gtk4',
'rav1e',
'tracers'
'rtp',
'rtsp',
'webrtc',
'webrtchttp',
]
super().prepare()