[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/api/utils/__tests__/compute-cursor-arg-filter.utils.spec.ts

@@ -101,7 +101,7 @@ describe('computeCursorArgFilter', () => {
     createdAt: new Date(),
     updatedAt: new Date(),
     universalIdentifier: objectMetadataId,
-    fieldMetadataIds: ['name-id', 'age-id', 'fullname-id'],
+    fieldIds: ['name-id', 'age-id', 'fullname-id'],
     indexMetadataIds: [],
     viewIds: [],
     applicationId: null,