wps: zombie processes

PyWPS does not perform cleanup of zombie processes. New processes are refused because of

Maximum number of parallel running processes reached. Please try later.

Zombie processes could be removed by

update pywps_requests set percent_done = -1 where percent_done < 100;

The WHERE statement should filter processes older than given threshold (eg. one day).

Can be implemented as cronjob in docker: https://gitlab.com/geoharmonizer_inea/web-processing/-/tree/master/wps

Or better systematically in PyWPS code (threshold could be given by config).