fix(metric_alerts): Process most recent incident snapshots first, and only fetch the amount we need. (#21347)
fix(metric_alerts): Process most recent incident snapshots first, and only fetch the amount we need. (#21347)

Two small fixes:
 - Process only recent snapshots first. These are less likely to be outside the valid range,
   although not guaranteed
 - Only fetch batch_size + 1 rows. We only ever process `batch_size` rows, and just need to fetch
   one extra row so that we know we have more pages to process.
beeftornado/sentry,beeftornado/sentry,beeftornado/sentry