Add SSH ProxyCommand for accessing VMs through a bastion/hypervisor

[MiguelCarpio]

What does this PR do?
Support for accessing VMs through a bastion host or hypervisor using SSH ProxyCommand, which is essential for environments where VMs are not directly accessible from the pod network (like gpu-validation pod). e. g. VMs with private network floating IPs that can be accessed through the host (gpu-validation pod can reach the host network). This PR does:

• Adds gpu_validation_ssh_proxy_command variable
• Provides a helpful example showing the syntax: -o ProxyCommand="ssh -W %h:%p -o StrictHostKeyChecking=no -i /path/to/key user@bastion-host"
• Defaults to empty (undefined), maintaining backward compatibility

The ProxyCommand uses the -W %h:%p flag, which tells SSH to forward the connection to the target host (%h) and port (%p) through the bastion, creating a transparent tunnel.

Why do we need this PR?
This is critical for environments where:

• VMs are on private networks (e.g., 192.168.x.x)
• Only the hypervisor/bastion has network access to the VMs
• Ansible is running from a remote machine (not the hypervisor itself)

[bogdando]

lgtm, it makes sense to have it

[csibbitt]

I'm okay with this, but I'm curious - is this needed in our lab environment for some reason, or are you just using this for development purposes?

[MiguelCarpio]

I'm okay with this, but I'm curious - is this needed in our lab environment for some reason, or are you just using this for development purposes?

@csibbitt We need this to allow the gpu-validation pod to reach the target VM, which is in a private network that is accessible from the host.