graphql: Add a filter by group

server/src/domain/handler.rs

@@ -48,8 +48,10 @@ pub enum RequestFilter {
     Or(Vec<RequestFilter>),
     Not(Box<RequestFilter>),
     Equality(String, String),
-    // Check if a user belongs to a group.
+    // Check if a user belongs to a group identified by name.
     MemberOf(String),
+    // Same, by id.
+    MemberOfId(GroupId),
 }
 
 #[derive(PartialEq, Eq, Debug, Serialize, Deserialize, Clone, Default)]