Postgres doesn't accept `\u0000` in the jsonb datatype. Switch to the
json datatype which is larger and slower, but accepts escaped null
bytes.
As we don't actually query or index the result jsonb directly, the
impact of this should be minimal.
See: https://www.postgresql.org/docs/current/datatype-json.html
If a job is unresponsive the worker has most likely crashed or been shut
down and the in-progress job been lost.
Instead of failing these jobs, requeue them up to two times. Once a job is lost
a third time it fails. This avoids infinite loops.
This is implemented by extending FinishJob to RequeuOrFinish job. It takes a
max number of requeues as an argument, and if that is 0, it has the same
behavior as FinishJob used to have.
If the maximum number of requeues has not yet been reached, then the running
job is returned to pending state to be picked up again.
This introduces an expiry date (default: 14 days from insert date) and
adjust the service-maintenance script to delete jobs that are older than
the expiration date.
