Prevent relation update from settings (#13099)

## Expected behavior

Described behavior regarding: (update | create) x (custom | standard) x
(icon, label, name, isSynced)

**Custom:**
- Field RELATION create: name, label, isSynced, icon should be editable
- Field RELATION update: name should not, icon label, isSynced should
- For other fields, icon, label, name, isSynced should be editable at
field creation | update

To simplify: Field RELATION name should not be editable at update

**Standards**
- Field: create does not makes sense
- Field: name should not, icon label, isSynced should (this will end up
in overrides)

To simplify, no Field RELATION edge case, name should not be editable at
update

**Note:** the FE logic is quite different as the UI is hiding some
details behind the syncWithLabel. See my comments and TODO there


## What I've tested:
(update | create) x (custom | standard) x (icon, label, name, isSynced,
description)

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

@@ -9,10 +9,10 @@ import {
   Max,
   Min,
   ValidationError,
-  isDefined,
   validateOrReject,
 } from 'class-validator';
 import { FieldMetadataType } from 'twenty-shared/types';
+import { isDefined } from 'twenty-shared/utils';
 
 import { FieldMetadataSettings } from 'src/engine/metadata-modules/field-metadata/interfaces/field-metadata-settings.interface';
 import { FieldMetadataInterface } from 'src/engine/metadata-modules/field-metadata/interfaces/field-metadata.interface';
@@ -187,5 +187,20 @@ export class FieldMetadataValidationService {
         settings: fieldMetadataInput.settings,
       });
     }
+
+    const isRelationField =
+      fieldMetadataType === FieldMetadataType.RELATION ||
+      fieldMetadataType === FieldMetadataType.MORPH_RELATION;
+
+    if (
+      isRelationField &&
+      isDefined(existingFieldMetadata) &&
+      fieldMetadataInput.name !== existingFieldMetadata.name
+    ) {
+      throw new FieldMetadataException(
+        'Name cannot be changed for relation fields',
+        FieldMetadataExceptionCode.INVALID_FIELD_INPUT,
+      );
+    }
   }
 }