Always sync alert escalation attributes to incidents

What does this MR do and why?

• Related issue: #356215 (closed)
• Related MR: !83159 (merged)

Together with !83787 (merged) & !83159 (merged), this MR resolves a bug in the incident escalations feature, which blocks rollout of the feature flag.

• Circumvents :incident_escalations feature flag to:
  • Persists escalation_status record when an incident is created from an alert.
  • Persists/updates a corresponding escalation_status record when an alert status is updated.
• Changes should be removable as part of removing the :incident_escalations feature flag
• Changes are not user-facing, so no changelog is included

How to set up and validate locally

!83787 (merged) goes through details of testing.

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.

Related to #356215 (closed)