Improve object metadata maps size (#8635)

## Context
The object metadata map is becoming quite large and its structure could
be simplified.
We are removing byNameSingular/byNamePlural keys, the former can be
retrieved through a new helper and the latter is not used in the code
base currently.

packages/twenty-server/src/engine/metadata-modules/utils/generate-object-metadata-maps.util.ts

@@ -9,8 +9,7 @@ export const generateObjectMetadataMaps = (
 ): ObjectMetadataMaps => {
   const objectMetadataMaps: ObjectMetadataMaps = {
     byId: {},
-    byNameSingular: {},
-    byNamePlural: {},
+    idByNameSingular: {},
   };
 
   for (const objectMetadata of objectMetadataCollection) {
@@ -29,10 +28,8 @@ export const generateObjectMetadataMaps = (
     };
 
     objectMetadataMaps.byId[objectMetadata.id] = processedObjectMetadata;
-    objectMetadataMaps.byNameSingular[objectMetadata.nameSingular] =
-      processedObjectMetadata;
-    objectMetadataMaps.byNamePlural[objectMetadata.namePlural] =
-      processedObjectMetadata;
+    objectMetadataMaps.idByNameSingular[objectMetadata.nameSingular] =
+      objectMetadata.id;
   }
 
   return objectMetadataMaps;