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/message-queue/jobs.module.ts

@@ -21,7 +21,6 @@ import { WorkspaceEntity } from 'src/engine/core-modules/workspace/workspace.ent
 import { WorkspaceModule } from 'src/engine/core-modules/workspace/workspace.module';
 import { AiAgentMonitorModule } from 'src/engine/metadata-modules/ai/ai-agent-monitor/ai-agent-monitor.module';
 import { AiChatModule } from 'src/engine/metadata-modules/ai/ai-chat/ai-chat.module';
-import { DataSourceModule } from 'src/engine/metadata-modules/data-source/data-source.module';
 import { LogicFunctionModule } from 'src/engine/metadata-modules/logic-function/logic-function.module';
 import { NavigationMenuItemModule } from 'src/engine/metadata-modules/navigation-menu-item/navigation-menu-item.module';
 import { ObjectMetadataModule } from 'src/engine/metadata-modules/object-metadata/object-metadata.module';
@@ -45,7 +44,6 @@ import { WorkflowModule } from 'src/modules/workflow/workflow.module';
 @Module({
   imports: [
     TypeOrmModule.forFeature([WorkspaceEntity, BillingSubscriptionEntity]),
-    DataSourceModule,
     ObjectMetadataModule,
     TypeORMModule,
     UserModule,