[Outbox.Memory] Deffer message publish form a unit of work until its finished

[zarusz]

This feature would include an in-memory outbox that is lean and fast.

The message published during a unit of work (HTTP request, message consumer) would be deferred until the unit of work finishes (e.g. Entity Framework SaveChanges()).

Customization points:

• The trigger to release the messages would be configurable (e.g. on EF DbContext SaveChanges, or others).
• It could be decided what transports and messages are subject to this behavior.