feat(ssh_host_keys): add role for managing SSH host keys

• Ensure the /tmp/ssh_keys directory exists.
• Download SSH host keys from S3 and unpack them to /etc/ssh.
• Restart the SSH service to apply the new keys.
• Add necessary variables for S3 and AWS credentials in groupvars/all.
• Include ssh_host_keys role in cluster.yml playbook.

merged manually