feat: kick-off event sourced tasks-svc

[MaxSchaefer]

This pull request starts our journey towards event sourcing and domain-driven-design in general. Therefore I've implemented libs/hwes that gets consumed by tasks-svc (and every other service that wants to utilizing event sourcing). libs/hwes introduces the concepts of Commands, Events, Aggregates and Aggregates stores. These concepts are implemented by tasks-svc, for example TaskAggregate or CreateTaskCommand or TaskCreatedEvent.

We already did a meeting on this new architecture but here is an outline:

1. Request gets handled by command or query (cq)
2. CQ loads the aggregate on which behalf to act on (by ID of aggregate)
   2.1 Create empty aggregate by the passed ID
   2.2 Load all events from the event store for that aggregate (every aggregate has its own event stream)
   2.3 Applying all events in order on the aggregate
3. CQ triggers business logic on aggregates that resolves in new uncommitted events
4. Before returning the request back to the caller of the CQ, persist all events in our event store.
   4.1 libs/hwes calculates the expected revision of the targeted event stream by combining the applied events of step 2. and the uncommitted events of step 3. .
   4.2.a If the revision cannot be reached due to concurrent changes to the targeted event stream the request fails.
   4.2.b If the revision can be reached during persistence, the events got stored successfully.

Step 4.2 describes optimistic concurrency. The application needs to keep track of versioning. We could apply all events, regarding there version but this can result in data conflicts and issues with idempotency. Its quite unlikely that Step 4.2.a occur but we need to keep track of this architecture trade-off with future metrics and tracing.

tasks-svc is not yet production ready. We can either integrate the event sourced task domain into the current task-svc or the other way around. Upcoming issues will work towards the production readiness.

To-dos for later issues

• Snapshots
• Projections and Subscriptions
• Identity context in events

Also closes #344

[FoseFx]

🥂