Remove sync-metadata and IS_WORKSPACE_CREATION_V2_ENABLED feature flag (#16997)

# Introduction
Followup of
https://github.com/twentyhq/twenty/pull/17001#pullrequestreview-3638508738
close https://github.com/twentyhq/core-team-issues/issues/1910

We've completely decom the `sync-metadata` in production. We're now then
removing its implementation in favor of the v2.

## TODO:
- [x] Remove sync-metadata implem and commands
- [x] Remove workspace decorators 
- [x] Type each deprecated field to deprecated on their workspaceEntity
- [x] Remove the `workspace-sync-metadata` folder entirely
- [x] remove workspace migration
- [x] workspace migration removal migration
- [x] remove the `v2` references from workspace manager file names
- [x] remove the `v2` references from workspace manager modules
- [ ] Double check impact on translation file path updates


## Note
- Removed the gate logic
- Remains some service v2 naming, serverless needs to be migrated on v2
fully
- Removed workspaceMigration service app health consumption, making it
always returning up ( no more down ) cc @FelixMalfait ( quite obsolete
health check now, will require complete refactor once we introduce inter
app dependency etc )

packages/twenty-server/src/engine/workspace-manager/dev-seeder/dev-seeder.module.ts

@@ -25,7 +25,7 @@ import { TimelineActivitySeederService } from 'src/engine/workspace-manager/dev-
 import { DevSeederMetadataService } from 'src/engine/workspace-manager/dev-seeder/metadata/services/dev-seeder-metadata.service';
 import { DevSeederService } from 'src/engine/workspace-manager/dev-seeder/services/dev-seeder.service';
 import { TwentyStandardApplicationModule } from 'src/engine/workspace-manager/twenty-standard-application/twenty-standard-application.module';
-import { WorkspaceMigrationV2Module } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-v2.module';
+import { WorkspaceMigrationModule } from 'src/engine/workspace-manager/workspace-migration/workspace-migration.module';
 
 @Module({
   imports: [
@@ -46,7 +46,7 @@ import { WorkspaceMigrationV2Module } from 'src/engine/workspace-manager/workspa
     ObjectPermissionModule,
     WorkspaceManyOrAllFlatEntityMapsCacheModule,
     WorkspaceCacheModule,
-    WorkspaceMigrationV2Module,
+    WorkspaceMigrationModule,
     TwentyStandardApplicationModule,
   ],
   exports: [DevSeederService],