Auto remove ponos containers

Refs https://support.teklia.com/t/workers-sexecutant-dans-une-infra-docker-separee-de-linstance-arkindex/73

We should introduce a setting to control if containers created by ponos agent tasks are automatically removed by Docker upon completion.

It would be disabled by default to allow for debugging.

Name: PONOS_DOCKER_AUTO_REMOVE_CONTAINER, set in ponos section