persistent mqtt messages

We need to have persistent client sessions with QoS>0 to prevent data loss due to temporarily not available services.

Directly related to issue tsm-orchestration#79 (closed)

• MQTT-Broker needs to be set to allow persistence
• pass QoS from docker compose to dispatcher workers via .env
• each worker needs to have a unique client_id and clean_session=false
• session expiration_date (or queue_size, ... ) needs to be defined to allow to close sessions that are inactive or whose queues grow too big