Stop panicking about short CDN blips
Stop panicking about short CDN blips

Previously we alerted for a short-lived spike in CDN 5xx rates,
which is unactionable. This smoothes out the spikes to avoid alerting
when there is no action to take.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet