Refactor flat entity maps to be universal oriented (#17665)

# Introduction
In preparation of the workspace agnostic builder, we're migrating
`FlatEntityMaps` to be universal identifier oriented and based
As in the builder context there're won't be any ids at all
Please also note that the FlatEntity is a UniversalFlatEntity superset

From
```ts
import { type SyncableFlatEntity } from 'src/engine/metadata-modules/flat-entity/types/flat-entity-from.type';

export type FlatEntityMaps<T extends SyncableFlatEntity> = {
  byId: Partial<Record<string, T>>;
  idByUniversalIdentifier: Partial<Record<string, string>>;
  universalIdentifiersByApplicationId: Partial<Record<string, string[]>>;
};
```

To
```ts
export type FlatEntityMaps<
  T extends SyncableFlatEntity | UniversalSyncableFlatEntity,
> = {
  byUniversalIdentifier: Partial<Record<string, T>>;
  universalIdentifierById: Partial<Record<string, string>>;
  universalIdentifiersByApplicationId: Partial<Record<string, string[]>>; // this might make more sense to be migrated to universalIdentifiersByApplicationUniversalIdentifier but it's the main topic of this PR
};
```

## Low level maps tools
Had to refactor find | create | delete | replace | find-many | get-sub
tools ( through mutations and or throw equivalent )

packages/twenty-server/src/engine/metadata-modules/page-layout-widget/services/page-layout-widget.service.ts

@@ -4,6 +4,7 @@ import { isDefined } from 'twenty-shared/utils';
 
 import { ApplicationService } from 'src/engine/core-modules/application/services/application.service';
 import { WorkspaceManyOrAllFlatEntityMapsCacheService } from 'src/engine/metadata-modules/flat-entity/services/workspace-many-or-all-flat-entity-maps-cache.service';
+import { findFlatEntityByIdInFlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/utils/find-flat-entity-by-id-in-flat-entity-maps.util';
 import { findFlatEntityByIdInFlatEntityMapsOrThrow } from 'src/engine/metadata-modules/flat-entity/utils/find-flat-entity-by-id-in-flat-entity-maps-or-throw.util';
 import { FlatPageLayoutWidgetMaps } from 'src/engine/metadata-modules/flat-page-layout-widget/types/flat-page-layout-widget-maps.type';
 import { FlatPageLayoutWidget } from 'src/engine/metadata-modules/flat-page-layout-widget/types/flat-page-layout-widget.type';
@@ -101,7 +102,7 @@ export class PageLayoutWidgetService {
     const flatPageLayoutWidgetMaps =
       await this.getFlatPageLayoutWidgetMaps(workspaceId);
 
-    return Object.values(flatPageLayoutWidgetMaps.byId)
+    return Object.values(flatPageLayoutWidgetMaps.byUniversalIdentifier)
       .filter(isDefined)
       .filter(
         (widget) =>
@@ -126,7 +127,10 @@ export class PageLayoutWidgetService {
     const flatPageLayoutWidgetMaps =
       await this.getFlatPageLayoutWidgetMaps(workspaceId);
 
-    const flatWidget = flatPageLayoutWidgetMaps.byId[id];
+    const flatWidget = findFlatEntityByIdInFlatEntityMaps({
+      flatEntityId: id,
+      flatEntityMaps: flatPageLayoutWidgetMaps,
+    });
 
     if (!isDefined(flatWidget) || isDefined(flatWidget.deletedAt)) {
       throw new PageLayoutWidgetException(
@@ -245,7 +249,10 @@ export class PageLayoutWidgetService {
     id: string,
     flatPageLayoutWidgetMaps: FlatPageLayoutWidgetMaps,
   ): FlatPageLayoutWidget {
-    const existingWidget = flatPageLayoutWidgetMaps.byId[id];
+    const existingWidget = findFlatEntityByIdInFlatEntityMaps({
+      flatEntityId: id,
+      flatEntityMaps: flatPageLayoutWidgetMaps,
+    });
 
     if (!isDefined(existingWidget) || isDefined(existingWidget.deletedAt)) {
       throw new PageLayoutWidgetException(