Fix/gtria 1126 available tickets

[andrasguseo]

🎫 Ticket

GTRIA-1126

🗒️ Description

The counting logic for the total number of available tickets on the attendees page did not account for shared capacity tickets correctly. All availability was added up instead of just adding the highest number of available tickets from the shared ones. The new code checks if the ticket is a shared capacity ticket or one with a cap, and collects those numbers in an array. After all other additions (single tickets) are done, the highest number from that array is added to the total available number.

🎥 Artifacts

Screenshot Screenshot with fix

✔️ Checklist

• [x] I've included a changelog entry in the readme.txt file.
• [ ] My code is tested.
• [x] Not relevant - My code has proper inline documentation.