fix: correctly infer objectFields type from props

Adjusted the ObjectField type definition to ensure that properties
present in Props are required and typed in the objectFields property.
This resolves an issue where properties were not being inferred, leading
to untyped fields.

Before:
<img width="422" alt="image"
src="https://github.com/measuredco/puck/assets/8417041/d690ae50-291a-4328-bc80-824873b14bca">

After:
<img width="774" alt="image"
src="https://github.com/measuredco/puck/assets/8417041/3d8f88b9-220a-4e80-9c7c-ba38eb14b583">

packages/core/types/Config.tsx

@@ -59,7 +59,7 @@ export type ObjectField<
 > = BaseField & {
   type: "object";
   objectFields: {
-    [SubPropName in keyof Props[0]]: Field<Props[0][SubPropName]>;
+    [SubPropName in keyof Props]: Field<Props[SubPropName]>;
   };
 };