give useful output when the Solr ConfigSet can't upload with auth

this script used to give output as though the SolrCloud instance was unreachable
when the authorization was unlocked. give some better information for debug
instead.

bin/solrcloud-upload-configset.sh

@@ -26,6 +26,10 @@ while [ $COUNTER -lt 30 ]; do
         (cd "$CONFDIR" && zip -r - *) | curl -X POST $solr_user_settings --header "Content-Type:application/octet-stream" --data-binary @- "$solr_config_upload_url"
       fi
       exit
+    else
+      echo "-- Solr at $solr_config_list_url is accepting unauthorized connections; we can't upload a trusted ConfigSet."
+      echo "--   It's possible SolrCloud is bootstrapping its configuration, so this process will retry."
+      echo "--   see: https://solr.apache.org/guide/8_6/configsets-api.html#configsets-upload"
     fi
   fi
   COUNTER=$(( COUNTER+1 ));