Fix author attachment field (#15065)

# Migrate Attachment Author to CreatedBy Field

**Twill Task**: https://twill.ai/twentyhq/ENG/tasks/7

## Summary

This PR implements a migration to transition the `Attachment` object
from using an `author` relation field to using the standard `createdBy`
field, addressing issue
https://github.com/twentyhq/core-team-issues/issues/1594.

## Changes

- **Added migration command**
(`1-8-migrate-attachment-author-to-created-by.command.ts`):
- Migrates existing attachment data to use `createdBy` instead of
`author`
- Ensures data integrity during the transition to the standard field
pattern

- **Updated Attachment workspace entity**:
  - Added `createdBy` relation field to the `Attachment` standard object
  - Registered new field ID in `standard-field-ids.ts` constants

- **Integrated migration into upgrade pipeline**:
  - Added migration module for version 1.8
  - Registered in the main upgrade version command module

This change aligns the `Attachment` object with Twenty's standard field
conventions by using the built-in `createdBy` field instead of a custom
`author` field.

---

Fixes https://github.com/twentyhq/core-team-issues/issues/1594

---------

Co-authored-by: Twill <agent@twill.ai>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Félix Malfait <felix.malfait@gmail.com>
Co-authored-by: Félix Malfait <felix@twenty.com>

packages/twenty-server/src/engine/workspace-manager/workspace-sync-metadata/constants/standard-field-ids.ts

@@ -33,6 +33,8 @@ export const ATTACHMENT_STANDARD_FIELD_IDS = {
   name: '20202020-87a5-48f8-bbf7-ade388825a57',
   fullPath: '20202020-0d19-453d-8e8d-fbcda8ca3747',
   type: '20202020-a417-49b8-a40b-f6a7874caa0d',
+  fileCategory: '20202020-8c3f-4d9e-9a1b-2e5f7a8c9d0e',
+  createdBy: '395be3bd-a5c9-463d-aafe-9bc3bbec3f15',
   author: '20202020-6501-4ac5-a4ef-b2f8522ef6cd',
   activity: '20202020-b569-481b-a13f-9b94e47e54fe',
   task: '20202020-51e5-4621-9cf8-215487951c4b',