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/api/graphql/workspace-schema.factory.ts

@@ -3,6 +3,7 @@ import { Injectable } from '@nestjs/common';
 import { makeExecutableSchema } from '@graphql-tools/schema';
 import { GraphQLSchema, printSchema } from 'graphql';
 import { gql } from 'graphql-tag';
+import { isDefined } from 'twenty-shared/utils';
 
 import { ScalarsExplorerService } from 'src/engine/api/graphql/services/scalars-explorer.service';
 import { workspaceResolverBuilderMethodNames } from 'src/engine/api/graphql/workspace-resolver-builder/factories/factories';
@@ -56,13 +57,13 @@ export class WorkspaceSchemaFactory {
       );
     }
 
-    const objectMetadataCollection = Object.values(objectMetadataMaps.byId).map(
-      (objectMetadataItem) => ({
+    const objectMetadataCollection = Object.values(objectMetadataMaps.byId)
+      .filter(isDefined)
+      .map((objectMetadataItem) => ({
         ...objectMetadataItem,
         fields: Object.values(objectMetadataItem.fieldsById),
         indexes: objectMetadataItem.indexMetadatas,
-      }),
-    );
+      }));
 
     // Get typeDefs from cache
     let typeDefs = await this.workspaceCacheStorageService.getGraphQLTypeDefs(