File storage cleaning (#18381)

- Remove feature flag
- Remove legacy methods in file-upload and file-service
- Migrate AI Chat to new file management

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Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-server/src/engine/twenty-orm/entity-manager/workspace-entity-manager.spec.ts

@@ -245,10 +245,7 @@ describe('WorkspaceEntityManager', () => {
         IS_RECORD_PAGE_LAYOUT_EDITING_ENABLED: false,
         IS_MARKETPLACE_ENABLED: false,
         IS_DATE_TIME_WHOLE_DAY_FILTER_ENABLED: false,
-        IS_FILES_FIELD_MIGRATED: false,
         IS_DRAFT_EMAIL_ENABLED: false,
-        IS_CORE_PICTURE_MIGRATED: false,
-        IS_OTHER_FILE_MIGRATED: false,
       },
       userWorkspaceRoleMap: {},
       eventEmitterService: {