TTL for unacknowledged messages

[ByteAlex]

Current behaviour:
When no worker is available messages are queued infinitely in the payload-server.

Desired behaviour:
Give a TTL on startup/command to the payload server, which will drop messages after the given TTL.

Possible other solution:
Give a max queue size to the payload-server. So after the queue size is reached, messages are dropped with FIFO, so the oldest messages are about to be forgot first.