[FEATURE] allow updating entry-event of a running multi-step journey

[JoernBerkefeld]

related to:

• [FEATURE] auto-pause and republish transactional send journeys during deploy #2031
• feature/2031 auto-pause & resume transactional journey to allow updating it… #2058

basically, when we want to update the entry event (sf-triggered, API event), then we tend to need a new version of the journey first and THEN we can fiddle with the event. at least that's what the GUI says.

Questions that need to be addressed:

• how does this effect the still running previous version?
• does the API even allow updating the event details in journey first?
• does the API allow updating the event after a new version was created? (the GUI doesn't actually save changes if there is no new journey version, despite allowing to make changes first)