Extend Public API to Support Triggering Event-Based Messages (e.g. Check-In Instructions)

Description:

We need to allow triggering event-based messages that are set up on demand (e.g. check-in instructions) through API.

Example use case:
We have a custom deposit collection solution for Booking.com guests. Once the guest makes their deposit, and the payment is confirmed, we want to trigger the check in instructions to be sent through Public API. Currently we have to trigger it manually