Improve operability of Notifications

[olebhansen]

Based on our current experience, Kafka seems to have been "overengineered". Look into if there are alternatives that will make the apps easier to operate and address ops-related issues.

Analysis and pre-requistites

Tasks

Beta Give feedback

1. POC: Implement synchronous interaction between Notification services #544
   kind/chore status/draft +2

Additional issues to be addressed and resolved

Tasks

Beta Give feedback

1. Consider how to handle notification that have been stuck in a sending state over time #323
   kind/chore status/draft +2
2. Consider how instances that face transient errors are handled #324
   kind/analysis status/draft +2
3. Implement health check for PostgreSQL #322
   kind/chore status/blocked status/draft +3