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-resolver-builder/workspace-resolver.factory.ts

@@ -1,6 +1,7 @@
 import { Injectable, Logger } from '@nestjs/common';
 
 import { IResolvers } from '@graphql-tools/utils';
+import { isDefined } from 'twenty-shared/utils';
 
 import { DeleteManyResolverFactory } from 'src/engine/api/graphql/workspace-resolver-builder/factories/delete-many-resolver.factory';
 import { DestroyManyResolverFactory } from 'src/engine/api/graphql/workspace-resolver-builder/factories/destroy-many-resolver.factory';
@@ -75,7 +76,9 @@ export class WorkspaceResolverFactory {
       Mutation: {},
     };
 
-    for (const objectMetadata of Object.values(objectMetadataMaps.byId)) {
+    for (const objectMetadata of Object.values(objectMetadataMaps.byId).filter(
+      isDefined,
+    )) {
       // Generate query resolvers
       for (const methodName of workspaceResolverBuilderMethods.queries) {
         const resolverName = getResolverName(objectMetadata, methodName);