We used make-wmf-branch/config.json to determine which repositories to process, but this has been deprecated (and, luckily, renamed so that RTB broke and I actually noticed this)
is now
https://phabricator.wikimedia.org/diffusion/MREL/browse/master/make-release/settings.yaml
For now I have hotpatched the bot to use a local copy of the deprecated json file, but we should convert soon-ish. I *think* the new wmf_core group is what we need.
It might be possible as well to reuse some of the Python codebase in make-release which parses the json file.