Support accessing Cloud Agents via Gateway

### What feature do you want to see added?

The scenario in question is that Jenkins is in one Datacenter on one network, and is creating build agents in a different datacenter on an internal network -- and the build agents are only accessible via a gateway. In SSH, there is a config file that specifies SSH Gateways as well as JumpHosts, but this plugin doesn't use that, or the OS supplied SSH module.
It would be cool if we could specify one of:

- SSH Proxy Host to use
- OS SSH module/program to use

### Upstream changes

_No response_