[Fix] fix timelineActivities on notes and tasks (#17814)

[Fixes
sentry](https://twenty-v7.sentry.io/issues/7238708876/?environment=prod&environment=prod-eu&project=4507072499810304&query=Field%20metadata%20for%20field&referrer=issue-stream&sort=date):
_Field metadata for field "targetTargetPersonId" is missing in object
metadata timelineActivity_

Regression caused by migration of note and task targets - fields were
renamed from personId to targetPersonId, impacting the event names,
while we still expected them in their previous shape.

---------

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Félix Malfait <FelixMalfait@users.noreply.github.com>

packages/twenty-server/src/engine/metadata-modules/object-metadata/utils/build-default-relation-flat-field-metadatas-for-custom-object.util.ts

@@ -90,10 +90,7 @@ export const buildDefaultRelationFlatFieldMetadatasForCustomObject = ({
             objectMetadataNameSingular,
           );
         const isFeatureFlagEnabled =
-          (objectMetadataNameSingular === 'timelineActivity' &&
-            existingFeatureFlagsMap[
-              FeatureFlagKey.IS_TIMELINE_ACTIVITY_MIGRATED
-            ]) ||
+          objectMetadataNameSingular === 'timelineActivity' ||
           (objectMetadataNameSingular === 'attachment' &&
             existingFeatureFlagsMap[FeatureFlagKey.IS_ATTACHMENT_MIGRATED]) ||
           (objectMetadataNameSingular === 'noteTarget' &&