Partially updates a support request. Supports setting the request
status and/or assignee. DoiT employees may set any of open,
pending, hold, or solved and may set the assignee; customers may
set only solved (parity with the console "mark as resolved" action)
and may not set an assignee. closed is not settable via the API
(Zendesk auto-closes from solved). The assignee is a DoiT-employee
email, resolved server-side to a Zendesk agent; an email that does not
resolve to an active agent returns 400. At least one mutable field
must be present. The response echoes the fields that were applied.