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/core-modules/key-value-pair/key-value-pair.entity.ts

@@ -25,7 +25,7 @@ export enum KeyValuePairType {
 }
 
 @Entity({ name: 'keyValuePair', schema: 'core' })
-@ObjectType('KeyValuePair')
+@ObjectType()
 @Unique('IndexOnKeyUserIdWorkspaceIdUnique', ['key', 'userId', 'workspaceId'])
 @Index('IndexOnKeyWorkspaceIdAndNullUserIdUnique', ['key', 'workspaceId'], {
   unique: true,