Add mutation for setting escalation policy on incidents

What does this MR do and why?

• Related issues: #330284 (closed), #332065 (closed)
• Dependent on: !76819 (merged)

This MR:

• Creates pending escalations for incidents when relevant policy or status updates occur
• Moves helpers for "open" statuses from AlertManagement::Alert into Escalatable module
• Adds sidekiq processing for issue escalations following same flow as for PendingEscalation::Alert

Overall flow:

There are a number of steps to updates to IncidentManagement::IssuableEscalationStatus records. These steps roughly follow the flowchart below. The area circled in red is the scope of this MR.

Sample inputs/outputs

Fetch

query issues {
  project(fullPath: "root/autodevops") {
    issues(types: INCIDENT) {
      nodes {
        iid
        title
        type
        escalationPolicy {
          id
	  name
        }
      }
    }
  }
}

{
  "data": {
    "project": {
      "issues": {
        "nodes": [
          {
            "iid": "194",
            "title": "trying again on new alert  - queue another",
            "type": "INCIDENT",
            "escalationPolicy": {
              "id": "gid://gitlab/IncidentManagement::EscalationPolicy/220",
              "name": "Testing"
            }
          },
          {
            "iid": "193",
            "title": "trying again on new alert  - queue another",
            "type": "INCIDENT",
            "escalationPolicy": null
          },
          {
            "iid": "192",
            "title": "trying again on new alert  - queue another",
            "type": "INCIDENT",
            "escalationPolicy": null
          }
        ]
      }
    }
  }
}

Update

mutation SetEscalationPolicy($update: IssueSetEscalationPolicyInput!) {
  issueSetEscalationPolicy(input: $update) {
    issue {
      iid
      title
      type
      escalationPolicy {
        id
        name
      }
    }
  }
}

Unsetting the policy

{
  "update": {
    "projectPath": "root/autodevops",
    "iid": "194",
    "escalationPolicyId": null
  }
}

{
  "data": {
    "issueSetEscalationPolicy": {
      "issue": {
        "iid": "194",
        "title": "trying again on new alert  - queue another",
        "type": "INCIDENT",
        "escalationPolicy": null
      }
    }
  }
}

Setting the policy

{
  "update": {
    "projectPath": "root/autodevops",
    "iid": "194",
    "escalationPolicyId": "gid://gitlab/IncidentManagement::EscalationPolicy/220"
  }
}

{
  "data": {
    "issueSetEscalationPolicy": {
      "issue": {
        "iid": "194",
        "title": "trying again on new alert  - queue another",
        "type": "INCIDENT",
        "escalationPolicy": {
          "id": "gid://gitlab/IncidentManagement::EscalationPolicy/220",
          "name": "Testing"
        }
      }
    }
  }
}

How to set up and validate locally

1. Follow the steps in !76819 (merged) add an IncidentManagement::IssuableEscalationStatus association to your incident
2. Open /-/graphql-explorer in your local env to run graphql queries/mutations like the samples above

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.