On quota reach, allow, per config, job submission with lower priority

[Olivier Sallou]

Per config, one could specify that if quota is reached, user can still submit jovs, but their priority is lowered.

[Olivier Sallou]

but prio is not managed by all schedulers (fifo for example) furthermore, prio is read from db, not task so cannot be modified directly. or should add a specific tag on task to put it at the end of the list (to go after all other pending jobs)