Include Icinga alerts in Slack message again
Include Icinga alerts in Slack message again

Now that we're timing the Icinga alerts to be every 6 months, we can
include it again to make sure we actually review the pages.

alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs