show source chain in error response message

Error messages in logs should generally be similar to the messages in
the response body now. There's a bit of a concern with the source chain
leaking sensitive information, but the errors that had a source were
generally already logging the second error in the chain in their own
Display impl, so if this is a problem it's unlikely to be a regression.

src/utils/error.rs

@@ -9,6 +9,7 @@ use ruma::{
     OwnedServerName,
 };
 use thiserror::Error;
+use wee_woo::ErrorExt;
 
 use crate::{observability::prelude::*, Ra};
 
@@ -117,7 +118,7 @@ impl Error {
             return Ra(UiaaResponse::MatrixError(error));
         }
 
-        let message = format!("{self}");
+        let message = format!("{}", self.display_with_sources(" -> "));
 
         let (kind, status_code) = match self {
             Self::BadRequest(kind, _) => (