s3-binary-cache: show the error's request ID

The request ID is essential for traceability and debugging purposes.
It allows us to connect client-side to server-side events.

src/libstore/s3-binary-cache-store.cc

@@ -48,7 +48,11 @@ R && checkAws(std::string_view s, Aws::Utils::Outcome<R, E> && outcome)
     if (!outcome.IsSuccess())
         throw S3Error(
             outcome.GetError().GetErrorType(),
-            s + ": " + outcome.GetError().GetMessage());
+            fmt(
+                "%s: %s (request id: %s)",
+                s,
+                outcome.GetError().GetMessage(),
+                outcome.GetError().GetRequestId()));
     return outcome.GetResultWithOwnership();
 }
 
@@ -121,9 +125,10 @@ class RetryStrategy : public Aws::Client::DefaultRetryStrategy
         checkInterrupt();
         auto retry = Aws::Client::DefaultRetryStrategy::ShouldRetry(error, attemptedRetries);
         if (retry)
-            printError("AWS error '%s' (%s), will retry in %d ms",
+            printError("AWS error '%s' (%s; request id: %s), will retry in %d ms",
                 error.GetExceptionName(),
                 error.GetMessage(),
+                error.GetRequestId(),
                 CalculateDelayBeforeNextRetry(error, attemptedRetries));
         return retry;
     }