Remove DataSourceService and clean up datasource migration logic (#19532)

## Summary

- **Drop the `objectMetadata.dataSourceId` foreign key and index** via a
1-22 fast instance command — column kept nullable for data preservation
- **Delete `DataSourceService`, `DataSourceModule`, and
`DataSourceException`** — all code now uses `workspace.databaseSchema`
directly
- **Remove `IS_DATASOURCE_MIGRATED` feature flag** from default flags
and all branching logic
- **Simplify workspace/object creation pipelines** —
`WorkspaceManagerService`, `DevSeederService`, and the object creation
action handler no longer route through `DataSourceService`
- **Keep `DataSourceEntity` and the `dataSource` table** for historical
data — entity stripped of all ORM relations

packages/twenty-server/src/engine/core-modules/auth/token/token.module.ts

@@ -16,7 +16,6 @@ import { UserWorkspaceEntity } from 'src/engine/core-modules/user-workspace/user
 import { UserEntity } from 'src/engine/core-modules/user/user.entity';
 import { WorkspaceEntity } from 'src/engine/core-modules/workspace/workspace.entity';
 import { CoreEntityCacheModule } from 'src/engine/core-entity-cache/core-entity-cache.module';
-import { DataSourceModule } from 'src/engine/metadata-modules/data-source/data-source.module';
 import { PermissionsModule } from 'src/engine/metadata-modules/permissions/permissions.module';
 import { WorkspaceCacheModule } from 'src/engine/workspace-cache/workspace-cache.module';
 
@@ -31,7 +30,6 @@ import { WorkspaceCacheModule } from 'src/engine/workspace-cache/workspace-cache
       ApplicationEntity,
     ]),
     TypeORMModule,
-    DataSourceModule,
     PermissionsModule,
     WorkspaceCacheModule,
     CoreEntityCacheModule,