Split bootstrap commands into system/toolchains/build-tools
This allows us to run the --system command in the docker file when building the image, and --toolchains and --build-tools when running a CI job.
This will simplify the job scripts, and will also allow us to test changes to the toolchain code in cerbero without rebuilding the image.
Needed for gst-ci!350 (merged).
Edited by Nirbheek Chauhan