Support ssh-key-dir on RHCOS 9

Description:

Upstream OKD/FCOS are already using latest ignition that supports [1] writing authorized keys in /home/core/.ssh/authorized_keys.d/ignition . With RHCOS 9, we should also start using new default path /home/core/.ssh/authorized_keys.d/ignition instead of /home/core/.ssh/authorized_keys

[1]https://github.com/openshift/machine-config-operator/pull/2688

Acceptance Criteria:

• ssh key gets written into /home/core/.ssh/authorized_keys.d/ignition on RHCOS 9 nodes and /home/co/.ssh/authorized_keys file doesn't exist
• Upgrade from RHCOS 8 to RHCOS 9 node works as expected and all ssh keys from /home/core/.ssh/authorized_keys gets migrated to /home/core/.ssh/authorized_keys.d/ignition
• MCO e2e test would have to adapt accordingly as today it is looking for ssh key in /home/core/.ssh/authorized_keys