Allow client provided starting job state
/cc @mupuf
Tarball state specfic parts and their dependencies pulled from https://gitlab.freedesktop.org/mupuf/valve-infra/-/merge_requests/116 and adjusted slightly.
I am foreshading the need for job tokens to be generated server side with the job_id_prefix, for now that is assumed unique.
Tests need some love.
Edited by Martin Roukala