[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/common/common-query-runners/common-create-many-query-runner/utils/__tests__/get-conflicting-fields.util.spec.ts

@@ -85,7 +85,7 @@ describe('getConflictingFields', () => {
       createdAt: new Date(),
       updatedAt: new Date(),
       universalIdentifier: objectMetadataId,
-      fieldMetadataIds: fields.map((f) => f.id),
+      fieldIds: fields.map((f) => f.id),
       indexMetadataIds: [],
       viewIds: [],
       applicationId: null,