Add escalation policy widget to incidents in GraphQL

What does this MR do and why?

Add escalation policy widget to incidents in GraphQL (#631727)

To migrate incidents to work item incidents, we need feature parity. We need to add incident-only widgets to work items so that when we view incidents in the work item detail view we can also see the incident widgets

Changelog: added

References

• #631727

Screenshots or screen recordings

How to set up and validate locally

1. Test that the escalation status is returned for an incident

query{
  namespace(fullPath:"flightjs/Flight") {
    workItem(iid:"60"){
      widgets {
        ... on WorkItemWidgetEscalationPolicy {
          type
          escalationPolicy {
            id
            name
          }
        }
      }
    }
  }
}

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.