Migrate noteTarget and taskTarget to Morph. (#17476)

This PR migrates `noteTarget` and `taskTarget` to morph relations behind
separate feature flags, following the Attachment/TimelineActivity
pattern.

It introduces the `IS_NOTE_TARGET_MIGRATED` and
`IS_TASK_TARGET_MIGRATED` flags, updates standard field metadata and
indexes to use morph relations, and adds two **1.17 workspace
migrations** that:
- rename `noteTarget.*Id` / `taskTarget.*Id` columns to `target*Id`
- convert the corresponding field metadata to `MORPH_RELATION` with a
shared `morphId`

On the frontend, note/task target read and write paths switch to
`target*Id` when the respective flag is enabled. Deleted targets are
filtered on reload to prevent reappearing relations.

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

@@ -32,8 +32,8 @@ const morphIdByRelationObjectNameSingular = {
     STANDARD_OBJECTS.timelineActivity.morphIds.targetMorphId.morphId,
   favorite: null,
   attachment: STANDARD_OBJECTS.attachment.morphIds.targetMorphId.morphId,
-  noteTarget: null,
-  taskTarget: null,
+  noteTarget: STANDARD_OBJECTS.noteTarget.morphIds.targetMorphId.morphId,
+  taskTarget: STANDARD_OBJECTS.taskTarget.morphIds.targetMorphId.morphId,
 } satisfies Record<
   (typeof DEFAULT_RELATIONS_OBJECTS_STANDARD_IDS)[number],
   string | null
@@ -97,6 +97,10 @@ export const buildDefaultRelationFlatFieldMetadatasForCustomObject = ({
             ]) ||
           (objectMetadataNameSingular === 'attachment' &&
             existingFeatureFlagsMap[FeatureFlagKey.IS_ATTACHMENT_MIGRATED]) ||
+          (objectMetadataNameSingular === 'noteTarget' &&
+            existingFeatureFlagsMap[FeatureFlagKey.IS_NOTE_TARGET_MIGRATED]) ||
+          (objectMetadataNameSingular === 'taskTarget' &&
+            existingFeatureFlagsMap[FeatureFlagKey.IS_TASK_TARGET_MIGRATED]) ||
           false;
         const isObjectMigratedToMorphRelations =
           isObjectMigratedFromOlderReleases || isFeatureFlagEnabled;