Displaysets not editable when Json-kind Interface is used

[miriam-groeneveld]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Go to a reader study that has a display set with a Json CIV.
2. Edit a display set that doesn't have a value for the Json CI
3. Save the display set
4. Now the displayset shows an added Json CI, but the value is null, causing a server error when trying to edit the display set.
5. See video and sentry error: https://grand-challenge.sentry.io/issues/5910158018/?project=303639&query=%21logger%3Acsp%20is%3Aunresolved&referrer=issue-stream&statsPeriod=24h&stream_index=0

Expected behavior
Display set should remain editable

Screenshots
https://github.com/user-attachments/assets/34d4a6eb-5abe-4d59-b66b-89aabf67a34f

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.

[amickan]

This is a general issue with the InterfaceFormField and how we handle/pass initial data to it. This is fixed by the refactoring done in #3465