[Actions] PagerDuty Resolve and Acknowledge payloads should contains only fields according to the API docs.

[YulNaumenko]

Currently we have a confusing UX for a PagerDuty action, when users are creating PagerDuty action to Resolve the incidents:
according to the UI and API requirements, user should enter Summary as a required field and can fill the other fields as an optional. But it won't work, because in PagerDuty API the allowed payload body should be for Resolve:

{
  "routing_key": "routingkeyhere",
  "dedup_key": "dedupkeyhere",
  "event_action": "resolve"
}

for Acknowledge:

{
  "routing_key": "routingkeyhere",
  "dedup_key": "dedupkeyhere",
  "event_action": "acknowledge"
}

If send the payload with some other fields, those won't be saved.

We should change the actions API schema body validation for a PagerDuty to support this use case and properly modify our UI to not show the rest of the fields, when Resolve or Acknowledge events was selected.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[pmuellr]

We should keep in mind the references to the "auto-recover action" functionality. Presumably if we have that, then the we would be creating the recover action, and so won't have to disable (or not show) the fields that can't be used. I'm kinda wondering if we should allow a customer to create a PD action (or other "auto-recover-able" actions) for the recovered action group at all. If we didn't allow that, then I'm not sure there's a case where we would need to disable|hide these fields at all.

[YulNaumenko]

We should keep in mind the references to the "auto-recover action" functionality. Presumably if we have that, then the we would be creating the recover action, and so won't have to disable (or not show) the fields that can't be used. I'm kinda wondering if we should allow a customer to create a PD action (or other "auto-recover-able" actions) for the recovered action group at all. If we didn't allow that, then I'm not sure there's a case where we would need to disable|hide these fields at all.

I still think that this issue should be addressed, because, except of the Resolved event in PagerDuty, we also have Acknowledge event, which also doesn't expect all that fields to be changed. It still will be confusing to the users that they are able to change the summary or any other field for Acknowledge, the same as for Resolved, which we probably replace in the future with "auto-recover action".