This should transactional snapshot isolation for `/sync` etc requests.
For now we don't use repeatable read due to some odd test failures with
invites.
Some tweaks for the send-to-device consumers/producers:
- use `json.RawMessage` without marshalling it first
- try further devices (if available) if we failed to `PublishMsg` in the
producers
- some logging changes (to better debug E2EE issues)
* Move receipt sending to own JetStream producer
* Move SendToDevice to producer
* Remove most parts of the EDU server
* Fix SendToDevice & copyrights
* Move structs, cleanup EDU Server traces
* Use HeadersOnly subscription
* Missing file
* Fix linter issues
* Move consumers to own files
* Rename durable consumer; Consumer cleanup
* Docs/config cleanup
