server: Add the attribute schema to the attributes in graphql

And make sure that we only request the schema once per top-level query

schema.graphql

@@ -1,6 +1,7 @@
 type AttributeValue {
   name: String!
   value: [String!]!
+  schema: AttributeSchema!
 }
 
 type Mutation {
@@ -152,10 +153,6 @@ type User {
   groups: [Group!]!
 }
 
-type AttributeList {
-  attributes: [AttributeSchema!]!
-}
-
 enum AttributeType {
   STRING
   INTEGER
@@ -163,6 +160,10 @@ enum AttributeType {
   DATE_TIME
 }
 
+type AttributeList {
+  attributes: [AttributeSchema!]!
+}
+
 type Success {
   ok: Boolean!
 }