New field creates fields widget field (#18022)

## Context
Introducing "NewFieldDefaultConfiguration" to FIELDS widget
configurations
```typescript
{
  isVisible: boolean;
  viewFieldGroupId: string | null;
}
```

This configuration will define where a new field should be added (which
section) and its default visibility inside FIELDS widget views.
The new field position should always be at the end (meaning the last
position for the view fields OR the last position of a viewFieldGroup)

See "New fields" on this screenshot
<img width="401" height="724" alt="Layout V1"
src="https://github.com/user-attachments/assets/4969bcaa-f244-4504-8947-778a02c24c47"
/>

packages/twenty-server/src/engine/workspace-manager/dev-seeder/core/utils/seed-feature-flags.util.ts

@@ -101,6 +101,11 @@ export const seedFeatureFlags = async ({
         workspaceId: workspaceId,
         value: true,
       },
+      {
+        key: FeatureFlagKey.IS_RECORD_PAGE_LAYOUT_EDITING_ENABLED,
+        workspaceId: workspaceId,
+        value: true,
+      },
     ])
     .execute();
 };