server: return user-defined attributes for groups in graphql

Part of #67

server/src/domain/model/group_attributes.rs

@@ -1,7 +1,7 @@
 use sea_orm::entity::prelude::*;
 use serde::{Deserialize, Serialize};
 
-use crate::domain::types::{GroupId, Serialized};
+use crate::domain::types::{AttributeValue, GroupId, Serialized};
 
 #[derive(Clone, Debug, PartialEq, DeriveEntityModel, Eq, Serialize, Deserialize)]
 #[sea_orm(table_name = "group_attributes")]
@@ -55,3 +55,18 @@ impl Related<super::GroupAttributeSchema> for Entity {
 }
 
 impl ActiveModelBehavior for ActiveModel {}
+
+impl From<Model> for AttributeValue {
+    fn from(
+        Model {
+            group_id: _,
+            attribute_name,
+            value,
+        }: Model,
+    ) -> Self {
+        Self {
+            name: attribute_name,
+            value,
+        }
+    }
+}