Fix ObjectType casing and conflict between Relation and RelationMetadata (#9849)

Fixes #9827 

Also uncovered a conflict with `@objectType('Relation')` and
`@objectType('relation)`

I don't want to address it in this PR so I will create a followup issue
when we close this but I think there's a confusion between
Relation/RelationMetadata, it's unclear what is what

---------

Co-authored-by: Antoine Moreaux <moreaux.antoine@gmail.com>

packages/twenty-server/src/engine/metadata-modules/relation-metadata/dtos/relation-metadata.dto.ts

@@ -24,7 +24,7 @@ registerEnumType(RelationMetadataType, {
   description: 'Type of the relation',
 });
 
-@ObjectType('relation')
+@ObjectType('RelationMetadata')
 @Authorize({
   authorize: (context: any) => ({
     workspaceId: { eq: context?.req?.workspace?.id },