> ~/.ssh # ls -al
You don't have any keys in ~/.ssh/
Either generate them, or mount /boot/config/ssh/ or /root/.ssh (ie wherever on host you have the keys) to container's /root/.ssh
Note in the parent post example you can see the example expects key to be found at ~/.ssh/id_rsa:
storage:
ssh_command: ssh -i /root/.ssh/id_rsa <-- keyfile for ssh
Yet your dir listing above shows there's no key to be found.