Per-alert descriptions fed to alerting integrations

[philpennock]

Is your feature request related to a problem? Please describe.

When the checkly alert comes to us via opsgenie, there's a lot of clicking to get through the dashboard and edit the alert to see what conditions led to a failure and then go checking internal playbooks for what went wrong.

Describe the solution you'd like

Per-alert "descriptions", as a freeform text field, which can be populated with whatever we think fit, and which are passed to the API of the alerting systems. Eg, in OpsGenie the new alert API has a "description" field with a 15,000 character limit. We'd like to be able to populate that with something other than View your failing check in the Checkly dashboard.

We'd then populate it with a concise human summary of what the alert is checking for, and a link to playbook documentation, to speed the time to comprehension when someone is woken up at 3am.

We might want multiple paragraphs for some situations, to have initial process checks be in the description. But we could live with a single paragraph if absolutely necessary. I've seen multiple paragraphs work very well in other monitoring systems.

Describe alternatives you've considered

Decorating elsewhere, which requires multiple sources of truth and a lot of complexity.

Additional context

Two existing issues relate to having descriptions, but not to the aspect of being able to pass that through to the alerting system and are more concerned with dashboard clutter. Those sound like short descriptions, not multiple paragraphs, else they'd just be a tab. So not the same. Those issues are: #241 and #133