Add SSH host keys management feature

[krishmoodbidri]

• Introduce new variables in group_vars/all for SSH host keys management:

  • enable_ssh_host_keys: Flag to enable/disable the feature
  • ssh_host_keys_s3_bucket: S3 bucket name for storing SSH host keys
  • ssh_host_keys_s3_object: Object name of the tar.gz file containing SSH host keys

• Update ohpc-build.yaml to include the new 'ssh_host_keys' role:

  • Add conditional execution based on enable_ssh_host_keys flag

• Create new role 'ssh_host_keys' with tasks to:

  • Download SSH host keys tar.gz from S3
  • Unpack the keys to /etc/ssh
  • Restart the SSH service