Add createdBy field on custom object creation (#6529)

In this PR, I'm:
- adding createdBy field (type ACTOR) on custom objects when created
- moving `name` and `position` default column to the set of columns
automatically creation on object creation
- fixing a bug on mutations (update / create), if the targetted object
has a 'data' custom field, it was conflicting with the payload ==> I
feel we need to refactor this part of the code but we can keep this for
a bit later as we plan to move out of pg_graphql

<img width="1198" alt="image"
src="https://github.com/user-attachments/assets/891c4a97-bab1-415c-8551-dabd5996a794">

packages/twenty-front/src/modules/object-record/utils/generateEmptyFieldValue.ts

@@ -90,6 +90,7 @@ export const generateEmptyFieldValue = (
     case FieldMetadataType.Actor: {
       return {
         source: 'MANUAL',
+        workspaceMemberId: null,
         name: '',
       };
     }