Fix graphql query createMany resolver with nested relations (#7061)

Looks like insert() does not return foreign keys. We could eventually
call findMany after but it seems that's what save() is doing so I'm
replacing insert with save.
```typescript
/**
 * Flag to determine whether the entity that is being persisted
 * should be reloaded during the persistence operation.
 *
 * It will work only on databases which does not support RETURNING / OUTPUT statement.
 * Enabled by default.
 */
reload?: boolean;
```

Note: save() also does an upsert by default with no way to configure
that so if we want to keep that behaviour we will need to add a check
before
```typescript
if (args.upsert) {
    const existingRecords = await repository.findBy({
      id: Any(args.data.map((record) => record.id)),
    });
    ...
```

---------

Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-server/src/engine/twenty-orm/factories/entity-schema-column.factory.ts

@@ -79,6 +79,7 @@ export class EntitySchemaColumnFactory {
         nullable: fieldMetadata.isNullable,
         createDate: key === 'createdAt',
         updateDate: key === 'updatedAt',
+        deleteDate: key === 'deletedAt',
         array: fieldMetadata.type === FieldMetadataType.MULTI_SELECT,
         default: defaultValue,
       };