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/twenty-orm/factories/workspace-datasource.factory.ts

@@ -166,15 +166,16 @@ export class WorkspaceDatasourceFactory {
             );
           } else {
             const entitySchemas = await Promise.all(
-              Object.values(cachedObjectMetadataMaps.byId).map(
-                (objectMetadata) =>
+              Object.values(cachedObjectMetadataMaps.byId)
+                .filter(isDefined)
+                .map((objectMetadata) =>
                   this.entitySchemaFactory.create(
                     workspaceId,
                     dataSourceMetadataVersion,
                     objectMetadata,
                     cachedObjectMetadataMaps,
                   ),
-              ),
+                ),
             );
 
             await this.workspaceCacheStorageService.setORMEntitySchema(

packages/twenty-server/src/engine/twenty-orm/repository/permissions.utils.ts

@@ -1,4 +1,6 @@
+import { isNonEmptyString } from '@sniptt/guards';
 import { ObjectRecordsPermissions } from 'twenty-shared/types';
+import { isDefined } from 'twenty-shared/utils';
 import { QueryExpressionMap } from 'typeorm/query-builder/QueryExpressionMap';
 
 import {
@@ -40,8 +42,23 @@ export const validateOperationIsPermittedOrThrow = ({
   const objectMetadataIdForEntity =
     objectMetadataMaps.idByNameSingular[entityName];
 
-  const objectMetadataIsSystem =
-    objectMetadataMaps.byId[objectMetadataIdForEntity]?.isSystem === true;
+  if (!isNonEmptyString(objectMetadataIdForEntity)) {
+    throw new PermissionsException(
+      PermissionsExceptionMessage.PERMISSION_DENIED,
+      PermissionsExceptionCode.PERMISSION_DENIED,
+    );
+  }
+
+  const objectMetadata = objectMetadataMaps.byId[objectMetadataIdForEntity];
+
+  if (!isDefined(objectMetadata)) {
+    throw new PermissionsException(
+      PermissionsExceptionMessage.PERMISSION_DENIED,
+      PermissionsExceptionCode.PERMISSION_DENIED,
+    );
+  }
+
+  const objectMetadataIsSystem = objectMetadata.isSystem === true;
 
   if (objectMetadataIsSystem) {
     return;