feat(forms): Allow form fields to be deleted and preserve value

[scttcper]

Right now if you want to preserve the value when adding and removing fields you would need to store the value outside the form model which defeats the purpose of the form model if you need another source of truth.

Adding preserveOnUnmount will help us use the form model in detectors. In the below video, we'd like to be able to preserve the model's value when switching between detector types.

https://github.com/user-attachments/assets/dd512ddb-9e55-449f-a5cd-0f244e747034