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-front/src/modules/object-metadata/graphql/mutations.ts

@@ -43,8 +43,10 @@ export const CREATE_ONE_FIELD_METADATA_ITEM = gql`
 `;
 
 export const CREATE_ONE_RELATION_METADATA_ITEM = gql`
-  mutation CreateOneRelationMetadata($input: CreateOneRelationInput!) {
-    createOneRelation(input: $input) {
+  mutation CreateOneRelationMetadataItem(
+    $input: CreateOneRelationMetadataInput!
+  ) {
+    createOneRelationMetadata(input: $input) {
       id
       relationType
       fromObjectMetadataId

packages/twenty-front/src/modules/object-metadata/graphql/queries.ts

@@ -2,8 +2,8 @@ import { gql } from '@apollo/client';
 
 export const FIND_MANY_OBJECT_METADATA_ITEMS = gql`
   query ObjectMetadataItems(
-    $objectFilter: objectFilter
-    $fieldFilter: fieldFilter
+    $objectFilter: ObjectFilter
+    $fieldFilter: FieldFilter
   ) {
     objects(paging: { first: 1000 }, filter: $objectFilter) {
       edges {