Add a temporary variable that can be replaced externally, via `sed` or
other mechanism.
Let our GitHub Actions workflow add the sha256sum of the built romfs.
finalize_helper
- check for a few more cases of user error (finalize (x).romfs)
- add error #25 if gm9 fails to boot (=gm9 does not exist = insufficient sd space)
finalize.gm9
- add logic to skip CIA installation