Create issue which is already associated with the alert

What does this MR do and why?

Related issue: #330284 (closed)

Associates alerts with incident issues on creation, rather than as a post-creation task. This allows the behavior in IssuableEscalationEtatuses/CreateService to be utilized from Issues::CreateService.

This is not user-facing.

How to set up and check for regressions locally

1. Open a project with an escalation policy in EE (Monitor > Escalation policies to create a policy)
2. Navigate to Settings > Monitor > Alerts > Current integrations
3. Create & enable a new HTTP Endpoint alert integration if none exist
4. For an existing integration, click > Send test alert to trigger a test with a sample payload, like this one:
   • {"title":"Triggering a test alert to associate with an incident"}
5. Navigate to Monitor > Alerts to find & open the detail view of the new of alert
6. Click Create incident & see that the incident got created
7. In rails console, check that the alert is associated with the incident & the escalation policy

   issue = Issue.last!
   issue.alert_management_alert #=> should be present
   issue.escalation_status.policy #=> should be present   

MR acceptance checklist

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