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/metadata-modules/object-metadata/object-metadata.entity.ts

@@ -2,8 +2,6 @@ import {
   Column,
   CreateDateColumn,
   Entity,
-  Index,
-  ManyToOne,
   OneToMany,
   PrimaryGeneratedColumn,
   type Relation,
@@ -12,7 +10,6 @@ import {
 } from 'typeorm';
 
 import { type WorkspaceEntityDuplicateCriteria } from 'src/engine/api/graphql/workspace-query-builder/types/workspace-entity-duplicate-criteria.type';
-import { DataSourceEntity } from 'src/engine/metadata-modules/data-source/data-source.entity';
 import { FieldMetadataEntity } from 'src/engine/metadata-modules/field-metadata/field-metadata.entity';
 import { IndexMetadataEntity } from 'src/engine/metadata-modules/index-metadata/index-metadata.entity';
 import { type ObjectStandardOverridesDTO } from 'src/engine/metadata-modules/object-metadata/dtos/object-standard-overrides.dto';
@@ -31,7 +28,6 @@ import { type JsonbProperty } from 'src/engine/workspace-manager/workspace-migra
   'namePlural',
   'workspaceId',
 ])
-@Index('IDX_OBJECT_METADATA_DATA_SOURCE_ID', ['dataSourceId'])
 export class ObjectMetadataEntity
   extends SyncableEntity
   implements Required<ObjectMetadataEntity>
@@ -39,7 +35,8 @@ export class ObjectMetadataEntity
   @PrimaryGeneratedColumn('uuid')
   id: string;
 
-  @Column({ nullable: false, type: 'uuid' })
+  // @deprecated - FK dropped, column kept for data preservation only
+  @Column({ nullable: true, type: 'uuid' })
   dataSourceId: string;
 
   @Column({ nullable: false })
@@ -120,11 +117,6 @@ export class ObjectMetadataEntity
   })
   indexMetadatas: Relation<IndexMetadataEntity[]>;
 
-  @ManyToOne(() => DataSourceEntity, (dataSource) => dataSource.objects, {
-    onDelete: 'CASCADE',
-  })
-  dataSource: Relation<DataSourceEntity>;
-
   @CreateDateColumn({ type: 'timestamptz' })
   createdAt: Date;