APIEngagementUpdateAutomationsModel

Automation changes for an existing engagement. Unlike APIEngagementAutomationsModel (used
at create time, where "not specified" and Manually are equivalent since there's nothing to preserve),
each trigger here is nullable and independent: null means "leave this automation unchanged", which is
a different, meaningful thing from explicitly setting it to Manually (which clears an existing one).

{
    "inProgress": null,
    "inProgressDate": null,
    "complete": null,
    "completeDate": null
}