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/dataloaders/dataloader.interface.ts

@@ -7,12 +7,16 @@ import {
   type MorphRelationLoaderPayload,
   type ObjectMetadataLoaderPayload,
   type RelationLoaderPayload,
+  type ViewFieldGroupsByViewIdLoaderPayload,
+  type ViewFieldsByViewFieldGroupIdLoaderPayload,
 } from 'src/engine/dataloaders/dataloader.service';
 import { type FieldMetadataDTO } from 'src/engine/metadata-modules/field-metadata/dtos/field-metadata.dto';
 import { type RelationDTO } from 'src/engine/metadata-modules/field-metadata/dtos/relation.dto';
 import { type IndexFieldMetadataDTO } from 'src/engine/metadata-modules/index-metadata/dtos/index-field-metadata.dto';
 import { type IndexMetadataDTO } from 'src/engine/metadata-modules/index-metadata/dtos/index-metadata.dto';
 import { type ObjectMetadataDTO } from 'src/engine/metadata-modules/object-metadata/dtos/object-metadata.dto';
+import { type ViewFieldGroupDTO } from 'src/engine/metadata-modules/view-field-group/dtos/view-field-group.dto';
+import { type ViewFieldDTO } from 'src/engine/metadata-modules/view-field/dtos/view-field.dto';
 
 export interface IDataloaders {
   relationLoader: DataLoader<RelationLoaderPayload, RelationDTO | null>;
@@ -41,4 +45,14 @@ export interface IDataloaders {
     ObjectMetadataLoaderPayload,
     ObjectMetadataDTO | null
   >;
+
+  viewFieldGroupsByViewIdLoader: DataLoader<
+    ViewFieldGroupsByViewIdLoaderPayload,
+    ViewFieldGroupDTO[]
+  >;
+
+  viewFieldsByViewFieldGroupIdLoader: DataLoader<
+    ViewFieldsByViewFieldGroupIdLoaderPayload,
+    ViewFieldDTO[]
+  >;
 }