[REQUEST] Alert Blacklist - exclude alerting for specific or regex metrics

It would be nice to be able to exclude certain graphite metrics from the alerts. E.g., I would create an alert for all filesystems but exclude /tmp.

No files, tests, or entry points are named in the issue. Start by locating how alert metrics are selected and configured, then determine how specific names and regular expressions should be represented; done means metrics such as /tmp can be excluded without suppressing other filesystem alerts.

Written by the indexing model from the issue text.