[Feature] Implement acknowledge mechanism

Implementing reliable job completion notifications to the producer of jobs is currently possible by using a producer queue where the consumer/worker puts the results of its processing. However requires boilerplate which should not be needed for such a common case. Instead we can have an extra option when adding a job, acknowledge where the producer can specify a results queue, where the consumer will automatically and reliably put the results. The acknowledge option could be a single string for specifying a queue name, but it could also be an object with queue name and redis connection string, for those cases where the results shall be placed in a different redis server.