Message bus integration has been removed from machina core, and now exists as plugins. For integration with postal.js, see machina.postal
Due to the above change, the only "messaging-related" metadata on an FSM now is the "namespace" value that can be passed as the FSM is created. This value is optional, and will be given a default if none is provided. Messaging plugins can utilize this value as a channel/namespace name and/or topic prefix.