Scope: write:maintenance

Does what cancelling a job in Loop does: the job becomes cancelled, with the date, the
reason and the cancelling agent in cancellation, and Loop's "Cancelled job … by …" note is
written. Its quotes are left as they are. Only a notAcknowledged, pending or approved
job can be cancelled, as in Loop; any other answers 409.

reason is required, up to 320 characters. userId is recorded as the cancelling agent,
must be in the job's team and defaults to its first agent. No emails are sent to the
contractor, landlord or tenant.