The configuration file is shared between debdeploy-client and wmf-auto-restarts, however chatting with @Muehlenhoff it has emerged that the config is really agnostic and both tools need it for restarts detection. It could be very well elsewhere that's not tied to debdeploy somewhere in /etc. This coupling has caused problems wrt hiera settings not working in cloudvps for example (T336845), though the coupling applies to production too