Refactor builder to embed Object validation create/delete/update (#13934)

# Introduction
Moving validation directly in the builder that has the perfect
granularity to do it.
When importing we won't have to infer and dispatch on the operation
nature ( update delete create ) and validate accordingly

## Objects
Only migrated object validation for the moment even though create object
involves a validate flat field metadata creation call too

## TODO
- improve `otherFlatObjectMetadataMapsToValidate` naming too vague

## Next
- handle fields validation within fields actions build
- Unit test coverage validation issue on builder and validate
- integration test plugging with new feature flag

## Manual tested
- Update
- Delete
- Create TODO

packages/twenty-server/src/engine/metadata-modules/flat-field-metadata/services/flat-field-metadata-validator.service.ts

@@ -266,6 +266,19 @@ export class FlatFieldMetadataValidatorService {
         ),
       );
     } else {
+      if (
+        isDefined(
+          parentFlatObjectMetadata.fieldsById[flatFieldMetadataToValidate.id],
+        )
+      ) {
+        errors.push(
+          new ObjectMetadataException(
+            'Field with same id already exists in object',
+            ObjectMetadataExceptionCode.OBJECT_MUTATION_NOT_ALLOWED,
+          ),
+        );
+      }
+
       if (parentFlatObjectMetadata.isRemote === true) {
         errors.push(
           new ObjectMetadataException(