fix(appointments): Write Talk link to event

[ChristophWurst]

How to test

0. Have Talk set up
1. Create an appointment config, enable the Talk link integration
2. Open the booking page
3. Book
4. Confirm
5. Open the event as organizer

main: Event has no location set
here: Event has location set to the Talk URL

[ChristophWurst]

/backport to stable4.5

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a8120b9) 24.67% compared to head (dcb2524) 24.67%.
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #5573   +/-   ##
=========================================
  Coverage     24.67%   24.67%           
  Complexity      406      406           
=========================================
  Files           241      241           
  Lines         10693    10693           
  Branches       1739     1739           
=========================================
  Hits           2639     2639           
  Misses         8054     8054           

Flag	Coverage Δ
javascript	15.67% <ø> (ø)
php	62.36% <ø> (ø)

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