Add Dapr service bus scale rule custom operation

[mattgallagher92]

containerApp builders already have support for add_custom_scale_rule, which I've used a few times to add service bus scale rules. I think that perhaps a specific add_service_bus_scale_rule operation could be useful too.

I hope to be able to contribute this in the next few weeks, just opening this issue in case anyone has comments before I raise a PR.

[mattgallagher92]

Relevant docs https://learn.microsoft.com/en-us/azure/container-apps/dapr-keda-scaling