Allow installing extra packages during ostree-commit/image build stage

For package-centric testing of ostree images, we need to be able to install packages listed in bin_pkg_list into the images, as we won’t be able to install them at the time of the test.

For this purpose, add two extra arguments, extra_packages to allow installing extra packages during ostree-commit/image build stage.

This MR is a dependency of tests/apertis-test-cases!606 (merged).