There is no way to specify the hostname field of the spec using the Deploy Kubernetes Containers step.
If you want full control over the k8s YAML, you can use the Deploy Raw Kubernetes YAML step, which allows you to supply the exact YAML.
Unfortunately we don’t have experience hosting RabbitMQ in Kubernetes, so we can’t provide any specific advice on how to configure this. I do wonder if there is a way to achieve it without directly specifying the pod hostname? I’m assuming that approach won’t work if you want multiple pods in a RabbitMQ cluster?
If there’s any help we can provide, don’t hesitate to ask.