use single global function for server name local and user local checking

Signed-off-by: strawberry <strawberry@puppygock.gay>

src/utils/user_id.rs

@@ -0,0 +1,8 @@
+//! utilities for doing things with UserId's / usernames
+
+use ruma::UserId;
+
+use crate::services;
+
+/// checks if `user_id` is local to us via server_name comparison
+pub(crate) fn user_is_local(user_id: &UserId) -> bool { user_id.server_name() == services().globals.config.server_name }