Add a non-ephemral confirmation after an event is created

[smnc]

Is your improvement request related to a problem? Please describe.
Since updating to slash commands, the event creation wizard only generates ephemeral user-feedback messages, including the confirmation after an event is created.

Describe the solution you'd like
The wizard should create a non-ephemeral confirmation message (with a time-stamp and the event ID)

Describe alternatives you've considered
None

Additional context
Other users have no way to know an event has been added without checking the calendar, and in addition the event ID has to be looked up if the ephemeral message is cleared.