[OBJECT_CACHE_FLUSH_REQUIRED_WHEN_RELEASED] Remove FlatObjectMetadata custom fieldMetadataIds fk aggregator property (#17438)

# Introduction
Currently refactoring `flatEntity` typing, encountering some tsc errors
due to this fk aggregator custom override
It shall now follow generic pattern leading to be named `fieldIds`

Needs to flush object cache when released

packages/twenty-server/src/engine/twenty-orm/entity-manager/workspace-entity-manager.spec.ts

@@ -107,7 +107,7 @@ describe('WorkspaceEntityManager', () => {
       isSystem: false,
       isActive: true,
       targetTableName: 'test_entity',
-      fieldMetadataIds: ['field-id'],
+      fieldIds: ['field-id'],
       indexMetadataIds: [],
       viewIds: [],
       universalIdentifier: 'test-entity-id',