Support costume host (instead of '*') for Spring Boot Starter.

Right now there is a way to config only the ports via:

kotlin: jupyter: kernel: ports: hb: 9091 shell: 9092 control: 9093 stdin: 9094 iopub: 9095 

For security reasons, I would like to specify a custom host as well, instead of using "*" (which binds to all interfaces). Ideally, it should default to "localhost" to restrict access.