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/workspace-manager/workspace-manager.service.ts

@@ -14,7 +14,6 @@ import {
 } from 'src/engine/core-modules/sdk-client/jobs/generate-sdk-client.job';
 import { UserWorkspaceEntity } from 'src/engine/core-modules/user-workspace/user-workspace.entity';
 import { WorkspaceEntity } from 'src/engine/core-modules/workspace/workspace.entity';
-import { DataSourceService } from 'src/engine/metadata-modules/data-source/data-source.service';
 import { RoleEntity } from 'src/engine/metadata-modules/role/role.entity';
 import { RoleService } from 'src/engine/metadata-modules/role/role.service';
 import { UserRoleService } from 'src/engine/metadata-modules/user-role/user-role.service';
@@ -28,7 +27,6 @@ export class WorkspaceManagerService {
 
   constructor(
     private readonly workspaceDataSourceService: WorkspaceDataSourceService,
-    private readonly dataSourceService: DataSourceService,
     @InjectRepository(UserWorkspaceEntity)
     private readonly userWorkspaceRepository: Repository<UserWorkspaceEntity>,
     private readonly roleService: RoleService,
@@ -65,10 +63,9 @@ export class WorkspaceManagerService {
 
     const dataSourceMetadataCreationStart = performance.now();
 
-    await this.dataSourceService.createDataSourceMetadata(
-      workspaceId,
-      schemaName,
-    );
+    await this.workspaceRepository.update(workspaceId, {
+      databaseSchema: schemaName,
+    });
 
     await this.applicationService.createTwentyStandardApplication({
       workspaceId,