Allow manual triggering of requeue_message

[tommairs]

There are times when an operator may want to have KumoMTA re-evaluate messages and requeue them based on new information.

• A campaign may have been assigned to the wrong queue and needs to be re-routed
• IPs for a queue source may need to be reallocated, causing queue management issues.
• You may want to dump an entire campaign or other identified mail stream to a queue with different throttle settings (or to null)

Ideally, the operator will have the ability to use requeue_messages exactly as documented, but have it triggered ad-hoc as opposed to waiting for a transient failure.

In practice, usage may look like this:

if msg:get_meta("campaign") == "Flash Sale - 10 minutes only" then manual_requeue_message ("queue","null") end

OR if msg:get_meta("campaign") == "Back to school" then manual_requeue_message ("tenant","customer_147") end

Where the manual action would take place immediately on all queued messages (Scheduled and Ready) and the parameter to change will be one of : queue routing_domain tenant campaign