Migrate backend event with additional properties to internal events

Problem

After we enabled the passing of additional properties to Internal Events via Additional internal event properties on Backend (#434504 - closed) we can't be 100% sure everything works correctly without having at least one event created that is using the additional properties.

Desired Outcome

At least one backend event is create to use one of the additional properties.

Proposed Solution

Migrate incident_management_incident_published and associated metrics to internal events and continue using the label property as before.

Verify triggered event exists with label property in snowplow. ServicePing is out of scope.