move kconfig checks out of pmbootstrap's config/__init__.py to pmaports.git

In the last team meeting we decided it makes more sense to move the kconfig checks to pmaports.git. This avoids the problem we currently have, that when we require a new option in edge, the kconfig check will fail on stable unless we also change the kernels there.

As format we figured a json file from which we strip comments before parsing in python (as python's json parser doesn't handle comments), would make sense. Then it looks almost the same as the current format.

This file should also be added to v22.06, so kconfig check still works there. For earlier releases pmbootstrap kconfig check will break, but that's fine, these are EOL anyway. Let's print an error that the file is missing on that branch in pmaports in that case.