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/feature-flag/enums/feature-flag-key.enum.ts

@@ -10,6 +10,5 @@ export enum FeatureFlagKey {
   IS_DASHBOARD_V2_ENABLED = 'IS_DASHBOARD_V2_ENABLED',
   IS_TIMELINE_ACTIVITY_MIGRATED = 'IS_TIMELINE_ACTIVITY_MIGRATED',
   IS_ROW_LEVEL_PERMISSION_PREDICATES_ENABLED = 'IS_ROW_LEVEL_PERMISSION_PREDICATES_ENABLED',
-  IS_WORKSPACE_CREATION_V2_ENABLED = 'IS_WORKSPACE_CREATION_V2_ENABLED',
   IS_IF_ELSE_ENABLED = 'IS_IF_ELSE_ENABLED',
 }

packages/twenty-server/src/engine/core-modules/feature-flag/feature-flag.entity.ts

@@ -12,7 +12,7 @@ import {
 
 import { UUIDScalarType } from 'src/engine/api/graphql/workspace-schema-builder/graphql-types/scalars';
 import { FeatureFlagKey } from 'src/engine/core-modules/feature-flag/enums/feature-flag-key.enum';
-import { WorkspaceRelatedEntity } from 'src/engine/workspace-manager/workspace-sync/types/workspace-related-entity';
+import { WorkspaceRelatedEntity } from 'src/engine/workspace-manager/types/workspace-related-entity';
 
 @Entity({ name: 'featureFlag', schema: 'core' })
 @ObjectType('FeatureFlag')