[FEATURE] publish journey should create transactionalEmail for transactional journeys

[JoernBerkefeld]

turns out, saving a new transactional journey actually does create the journey without the transacionalEmail record being created. However, if we then hit publish, it runs a POST to

/interaction/v1/interactions/transactional/create
with payload {"definitionId":"fba40e55-c648-4d00-84c9-a66901a08a7c"}
The definitionId here is the ID of the journey
THAT then creates the transactionalEmail record in the background.

with this approach, both the journey key AND the tranactionalEmail key can be defined manually - contrary to creating a journey automatically when creating a transactionalEmail via API

[github-actions]

Closed by #1596.