Fix and refactor relation field name collision validation (#15920)

# Introduction
Fixes https://github.com/twentyhq/private-issues/issues/371
We weren't strictly validating relation field collision on join column
name availability of the target field object

## Refactor
Extracted morph or relation specific condition out of the common flat
field metadata name validate availability to be located in the dedicated
morph or relation flat field validator

## Tests
Added two tests, ONE_TO_MANY and MANY_TO_ONE in order to cover the use
case

packages/twenty-server/src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/validators/services/flat-field-metadata-validator.service.ts

@@ -131,7 +131,7 @@ export class FlatFieldMetadataValidatorService {
       validationResult.errors.push(
         ...validateFlatFieldMetadataName(flatFieldMetadataToValidate.name),
         ...validateFlatFieldMetadataNameAvailability({
-          flatFieldMetadata: flatFieldMetadataToValidate,
+          name: flatFieldMetadataToValidate.name,
           flatFieldMetadataMaps: optimisticFlatFieldMetadataMaps,
           flatObjectMetadata,
         }),
@@ -152,6 +152,7 @@ export class FlatFieldMetadataValidatorService {
     const fieldMetadataTypeValidationErrors =
       await this.flatFieldMetadataTypeValidatorService.validateFlatFieldMetadataTypeSpecificities(
         {
+          updates,
           optimisticFlatEntityMapsAndRelatedFlatEntityMaps: {
             flatFieldMetadataMaps: optimisticFlatFieldMetadataMaps,
             flatObjectMetadataMaps,
@@ -313,9 +314,8 @@ export class FlatFieldMetadataValidatorService {
 
       validationResult.errors.push(
         ...validateFlatFieldMetadataNameAvailability({
-          flatFieldMetadata: flatFieldMetadataToValidate,
+          name: flatFieldMetadataToValidate.name,
           flatFieldMetadataMaps: optimisticFlatFieldMetadataMaps,
-          remainingFlatEntityMapsToValidate,
           flatObjectMetadata: parentFlatObjectMetadata,
         }),
       );