Add get_event_by_calendar_appointment

[bensteUEM]

In order to retrieve an event for a particular calendar id the respective link needs to be established. At present /calendar endpoint does not offer any link information /events endpoint does mention calendar

"name": "Gottesdienst Friedrichstal" "appointmentId": 304973, "startDate": "2023-11-26T08:00:00Z",

but this could be problematic in case of multiple events created at the same time (happens from time to time with CT bugs)

• [x] Check with CT forum if there is an endpoint which would not require a workaround
• [x] implement workaround checking for events at same time as appointment that match appointment Id
• [x] consider matching name and caption - however these seem to be independant!