What is this feature?
This PR fixes the MissingSeriesEvalsToResolve behavior when it's set to more than 4 evaluation intervals.
Why do we need this feature?
The MissingSeriesEvalsToResolve setting was not working correctly due to alerts being auto-resolved by Alertmanager after 4 evaluation intervals (via the endsAt field).
Before we had deleteStaleStatesFromCache method that was returning only stale states that had to be resolved. Non-stale states for which the current evaluation does not have a series never had endsAt updated and were never resend to the Alertmanager, so they were automatically resolved after 4 evaluations regardless of the setting.
The new processMissingSeriesStates returns state for each missing series on every evaluation, and resolves the stale ones. This guarantees that alerts without series still alert for the configured number of evaluations.
Alexander Akhmetov
eae77aa695