Allow selection of egress port during a rebind

[tommairs]

As a mailops engineer, I want the ability to re-route message queues to other nodes for maintenance operations. The instructions here: https://docs.kumomta.com/userguide/clustering/scaling/#draining-the-spool-before-shutdown include the ability to set the routing_domain to another host by IP address which is helpful.
rebind --everything --set 'routing_domain=[192.168.1.100]'
However, this assumes the message will route using port 25. If my listeners listen on a different port, I need to be able to specify the port and I cannot currently do that. The command below will be interpreted as a string and will not deliver.
rebind --everything --set 'routing_domain=[192.168.1.100:2525]'

To make it work today, I need to have previously configured shaping to [192.168.1.100] to use smtp_port 2525.
My preference would be to set the port "on-the-fly".

One suggestion is to add "smtp_port" to the list of settings available in the rebind command.
IE: rebind --everything --set 'routing_domain=[192.168.1.100]' --set 'smtp_port=2525'