Relationships field in Form Builder

### Describe the feature you'd like to request

- Relationship field missing in generated UI forms.

### Describe the solution you'd like

- Enable support for relationships in Form Builder.

### Describe alternatives you've considered

- I have not found any alternative for UI forms.
- I tried to add custom field but relationship field also missing in mapping.

### Additional context

The form builds correctly but misses the relationship fields which are required fields for the CRUD mutations, so the mutation fails when using the component.

The issue names no files, tests, or entry points. Start by reproducing the missing relationship field in the Form Builder and tracing how generated forms map fields to CRUD mutations. Done means relationship fields appear in generated UI forms and the required CRUD mutations no longer fail.

Written by the indexing model from the issue text.