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/core-modules/applicationVariable/application-variable.entity.ts

@@ -1,5 +1,6 @@
 import { ObjectType } from '@nestjs/graphql';
 
+import { IDField } from '@ptc-org/nestjs-query-graphql';
 import {
   Column,
   CreateDateColumn,
@@ -10,12 +11,10 @@ import {
   Unique,
   UpdateDateColumn,
 } from 'typeorm';
-import { IDField } from '@ptc-org/nestjs-query-graphql';
-
-import { Relation } from 'src/engine/workspace-manager/workspace-sync-metadata/interfaces/relation.interface';
 
 import { UUIDScalarType } from 'src/engine/api/graphql/workspace-schema-builder/graphql-types/scalars';
 import { ApplicationEntity } from 'src/engine/core-modules/application/application.entity';
+import { EntityRelation } from 'src/engine/workspace-manager/workspace-migration/types/entity-relation.interface';
 
 @Entity({
   name: 'applicationVariable',
@@ -55,7 +54,7 @@ export class ApplicationVariableEntity {
     },
   )
   @JoinColumn({ name: 'applicationId' })
-  application: Relation<ApplicationEntity> | null;
+  application: EntityRelation<ApplicationEntity> | null;
 
   @CreateDateColumn({ type: 'timestamptz' })
   createdAt: Date;