Add option for max failures to sshpiper cmd in sshpiperd service file

The sshpiper failtoban plugin has two options. We currently only have ban-duration set to 20min, but didn't have max-failures options in code anywhere right now.

The task we discussed was simply just put the option in code as variable so if we need to change it in the future, we can do it easily.

https://github.com/tg123/sshpiper/tree/master/plugin/failtoban/README.md (edited)

https://github.com/jprorama/CRI_XCBC/blob/dev/roles/ssh_proxy/templates/sshpiperd.service.j2#L7

Related PR: https://github.com/jprorama/CRI_XCBC/pull/510