[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/repository/__tests__/workspace.repository.spec.ts

@@ -167,7 +167,7 @@ describe('WorkspaceRepository', () => {
         id: 'test-metadata-id',
         nameSingular: 'test-entity',
         namePlural: 'test-entities',
-        fieldMetadataIds: ['test-field-id'],
+        fieldIds: ['test-field-id'],
         fieldIdByName: {
           id: 'test-field-id',
         },