Add sync events

[cquintana92]

This PR performs the following changes:

1. Adds a new proto/events.proto file that defines events that a party may want to consume.
2. Adds a new app/events/event_listener.py that exposes an EventListener for dispatching events from within the app.
3. Adds a new event_listener.py entrypoint that can act as an event consumer or as a dead-letter consumer for the pending events.
4. Adds the event emit calls within the code.