api: add include_unset parameter to get_job and get_jobs

This allows to fetch the job with all the fields set, even if they were not passed (default), and to get it also only with the fields that were set on creation, so we can both show the user all the currently operational field values (ex. jobs list, jobs show) or just return the minimal parameters to create the job (ex. for jobs dump).

Bug: T402569
Depends-on: jobs-cli!124 (merged)
Signed-off-by: David Caro dcaro@wikimedia.org