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/middlewares/middleware.module.ts

@@ -1,17 +1,13 @@
 import { Module } from '@nestjs/common';
 
 import { TokenModule } from 'src/engine/core-modules/auth/token/token.module';
-import { FeatureFlagModule } from 'src/engine/core-modules/feature-flag/feature-flag.module';
 import { JwtModule } from 'src/engine/core-modules/jwt/jwt.module';
-import { DataSourceModule } from 'src/engine/metadata-modules/data-source/data-source.module';
 import { WorkspaceManyOrAllFlatEntityMapsCacheModule } from 'src/engine/metadata-modules/flat-entity/services/workspace-many-or-all-flat-entity-maps-cache.module';
 import { MiddlewareService } from 'src/engine/middlewares/middleware.service';
 import { WorkspaceCacheStorageModule } from 'src/engine/workspace-cache-storage/workspace-cache-storage.module';
 
 @Module({
   imports: [
-    DataSourceModule,
-    FeatureFlagModule,
     WorkspaceCacheStorageModule,
     WorkspaceManyOrAllFlatEntityMapsCacheModule,
     TokenModule,