event notifications

[opqdonut]

for #2095

Definition of Done / Review checklist

Reviewability

• link to issue

API

• API is documented and shows up in Swagger UI
• API is backwards compatible or completely new
• Events are backwards compatible

Documentation

• update changelog if necessary
• add or update docstrings for namespaces and functions
• documentation at least for config options (i.e. docs folder)
• ADR for major architectural decisions or experiments

Testing

• complex logic is unit tested
• valuable features are integration / browser / acceptance tested automatically

Follow-up

• no critical TODOs left to implement

[Macroz]

I wonder if it would make sense to log a bit more info here about the event itself too, like id.

[opqdonut]

hmm it looks like we don't pass the event id out of the db layer. I'll log the time, type, application-id.

[opqdonut]

clarification: these events don't have ids because they're directly from the command handler, not fetched from the db

[Macroz]

I think it'd make sense for the notified party to know the event id. It makes idempotency a bit easier.

[Macroz]

Looks good now. We can continue the discussions elsewhere, in followup PRs perhaps.