Introducing view field group syncable entity (#17867)

## Context
Introduces a new viewFieldGroup entity that allows grouping view fields
into sections (e.g. "General", "Additional", "Other") within a view.

The page layout fields widget needs a way to organize fields into
sections. Today, views have no concept of field grouping. This PR
introduces the viewFieldGroup entity which sits between a view and its
viewFields, enabling section-based organization.

<img width="401" height="724" alt="Layout - V2 (customize visibility)"
src="https://github.com/user-attachments/assets/6376e2ab-44db-42bf-9d2c-758f56f6b548"
/>

---------

Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-server/src/engine/metadata-modules/view-field/services/view-field.service.ts

@@ -27,7 +27,7 @@ import { WorkspaceMigrationBuilderException } from 'src/engine/workspace-manager
 import { WorkspaceMigrationValidateBuildAndRunService } from 'src/engine/workspace-manager/workspace-migration/services/workspace-migration-validate-build-and-run-service';
 
 @Injectable()
-export class ViewFieldV2Service {
+export class ViewFieldService {
   constructor(
     private readonly workspaceMigrationValidateBuildAndRunService: WorkspaceMigrationValidateBuildAndRunService,
     private readonly workspaceManyOrAllFlatEntityMapsCacheService: WorkspaceManyOrAllFlatEntityMapsCacheService,
@@ -76,11 +76,15 @@ export class ViewFieldV2Service {
         },
       );
 
-    const { flatFieldMetadataMaps, flatViewMaps } =
+    const { flatFieldMetadataMaps, flatViewMaps, flatViewFieldGroupMaps } =
       await this.workspaceManyOrAllFlatEntityMapsCacheService.getOrRecomputeManyOrAllFlatEntityMaps(
         {
           workspaceId,
-          flatMapsKeys: ['flatFieldMetadataMaps', 'flatViewMaps'],
+          flatMapsKeys: [
+            'flatFieldMetadataMaps',
+            'flatViewMaps',
+            'flatViewFieldGroupMaps',
+          ],
         },
       );
 
@@ -91,6 +95,7 @@ export class ViewFieldV2Service {
           flatApplication: workspaceCustomFlatApplication,
           flatFieldMetadataMaps,
           flatViewMaps,
+          flatViewFieldGroupMaps,
         }),
     );
 
@@ -146,17 +151,21 @@ export class ViewFieldV2Service {
         },
       );
 
-    const { flatViewFieldMaps: existingFlatViewFieldMaps } =
+    const {
+      flatViewFieldMaps: existingFlatViewFieldMaps,
+      flatViewFieldGroupMaps,
+    } =
       await this.workspaceManyOrAllFlatEntityMapsCacheService.getOrRecomputeManyOrAllFlatEntityMaps(
         {
           workspaceId,
-          flatMapsKeys: ['flatViewFieldMaps'],
+          flatMapsKeys: ['flatViewFieldMaps', 'flatViewFieldGroupMaps'],
         },
       );
 
     const optimisticallyUpdatedFlatView =
       fromUpdateViewFieldInputToFlatViewFieldToUpdateOrThrow({
         flatViewFieldMaps: existingFlatViewFieldMaps,
+        flatViewFieldGroupMaps,
         updateViewFieldInput,
       });