Update a request

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.