Extend the Sync Protocol's PostFlight step to indicate if policies blocking system critical binaries were pushed

[pmarkowsky]

The sync protocol's PostFlight step should be extended for a client to indicate that it received an unenforceable rule.

In some situations a sync service might push a policy for a critical system binary. In those cases Santa does not apply the policy.

The caveat is that the sync service does not have any feedback mechanism that such a rule was sent.