Fix relation field unknown target object (#13129)

Fixes https://github.com/twentyhq/twenty/issues/12867

Issue:
when you have a variable `toto` which is: `Record<string, MyType>` and
you do toto['xxx'], this will be typed as `MyType` instead of `MyType |
undefined`

Solutions:
- activate `noUncheckedIndexedAccess` check in tsconfig, this is the
preferred solution but will take time to get there (this raises 600+
errors)
- use a Map: cf https://github.com/twentyhq/twenty/pull/13125/files
- set the type to Partial<Record<string, MyType>>. Drawback is that when
you do Object.values(toto), you'll get `Array<MyType | undefined>`.
Hence why we have to filter these behind


<img width="1512" alt="image"
src="https://github.com/user-attachments/assets/d0a0bfed-c441-4e53-84c2-2da98ccbcf50"
/>

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

@@ -2,7 +2,7 @@ import { Injectable } from '@nestjs/common';
 import { InjectRepository } from '@nestjs/typeorm';
 
 import { FieldMetadataType } from 'twenty-shared/types';
-import { capitalize } from 'twenty-shared/utils';
+import { capitalize, isDefined } from 'twenty-shared/utils';
 import { QueryRunner, Repository } from 'typeorm';
 import { v4 as uuidV4 } from 'uuid';
 
@@ -82,10 +82,12 @@ export class ObjectMetadataFieldRelationService {
     relationObjectMetadataStandardId: string;
     queryRunner?: QueryRunner;
   }) {
-    const targetObjectMetadata = Object.values(objectMetadataMaps.byId).find(
-      (objectMetadata) =>
-        objectMetadata.standardId === relationObjectMetadataStandardId,
-    );
+    const targetObjectMetadata = Object.values(objectMetadataMaps.byId)
+      .filter(isDefined)
+      .find(
+        (objectMetadata) =>
+          objectMetadata.standardId === relationObjectMetadataStandardId,
+      );
 
     if (!targetObjectMetadata) {
       throw new Error(