As a visitor I want to know if a program I want to see is full, or when places in it are freed

Store the information in `program_v2.Program`, allow read/write access to it via GraphQL.

Make a visitor-visible feed in Kompassi on an info screen or similar with entries like:

- Cancelled: XX in YY at HH:MM
- Full: XX in YY at HH:MM
- Seats have become available again: XX in YY at HH:MM

Where does the information come from?

- Program manager sets it manually via program admin
- Security guard at the door sets it manually using mobile web page / PWA
- Konsti sets it via GraphQL API
- Paikkala sets it directly inside the backend
- A robot looks at the program hall with its electronic eyes (machine vision), determines when it is full and sets it via GraphQL API