By attaching external labels before relabelling, they are available during relabelling.
in case of dropping don't even enqueue them
This commit extends the notifier to dispatch alert batches to multiple Alertmanagers concurrently. It changes the `-alertmanager.url` flag to accept a comma separated list of URLs and/or to be set multiple times.
Frederic Branczyk
Tobias Schmidt
Fabian Reinartz