Resolved alerts, even when filtered, have to end up in the
SetNotifiesStage, otherwise when an alert fires again it is ambiguous
whether it was resolved in between or not.
fixes#523
This commit replaces the previous NotifyInfo provider with the new
nflog package. It needs adjustments in the behavior of the deduping
stage.
The nflog stores notification digests per receiver per alert aggregation
group rather than one entry for alert per receiver. This drastically
reduces the number of entries and removes interference
across aggregation groups.
Initial testing has shown BoltDB in plain usage to be a bottleneck
at a few thousand alerts or more (especially JSON decoding.
This commit actually makes them purely memory as a temporary solution.
This commit changes the notification grouping behavior
to simply send all alerts of a group as soon as a single
one of them needs updating.
This fixes a critical bug which caused erroneous resolved
notifications to be sent.
