fix: updated dryrun to return correct populated record (#15484)

## Description

- This PR approaches to solve
https://github.com/twentyhq/twenty/issues/15201
- updated `createDryRunResponse` to return fully populated merged record
- this way the frontend can render the populated data it as-is without
recomputing relations
- Dry-run now uses the same nested-relations population path as the
non-dryRun flow

---------

Co-authored-by: Etienne <45695613+etiennejouan@users.noreply.github.com>

packages/twenty-server/src/engine/api/graphql/graphql-query-runner/utils/merge-field-values.util.ts

@@ -1,4 +1,4 @@
-import { FieldMetadataType } from 'twenty-shared/types';
+import { FieldMetadataType, type RelationType } from 'twenty-shared/types';
 
 import { type EmailsMetadata } from 'src/engine/metadata-modules/field-metadata/composite-types/emails.composite-type';
 import { type LinksMetadata } from 'src/engine/metadata-modules/field-metadata/composite-types/links.composite-type';
@@ -8,18 +8,32 @@ import { mergeArrayFieldValues } from './merge-array-field-values.util';
 import { mergeEmailsFieldValues } from './merge-emails-field-values.util';
 import { mergeLinksFieldValues } from './merge-links-field-values.util';
 import { mergePhonesFieldValues } from './merge-phones-field-values.util';
+import { mergeRelationFieldValuesForDryRunRecord } from './merge-relation-field-values-for-dry-run-record.util';
 import { selectPriorityFieldValue } from './select-priority-field-value.util';
 
 export const mergeFieldValues = (
   fieldType: FieldMetadataType,
   recordsWithValues: { value: unknown; recordId: string }[],
   priorityRecordId: string,
+  isDryRun = false,
+  relationType?: RelationType,
 ): unknown => {
   switch (fieldType) {
     case FieldMetadataType.ARRAY:
     case FieldMetadataType.MULTI_SELECT:
       return mergeArrayFieldValues(recordsWithValues);
 
+    case FieldMetadataType.RELATION:
+      if (isDryRun) {
+        return mergeRelationFieldValuesForDryRunRecord(
+          recordsWithValues,
+          relationType,
+          priorityRecordId,
+        );
+      }
+
+      return selectPriorityFieldValue(recordsWithValues, priorityRecordId);
+
     case FieldMetadataType.EMAILS:
       return mergeEmailsFieldValues(
         recordsWithValues as { value: EmailsMetadata; recordId: string }[],