Replace rsyslog for non-bootstrap agents

This PR uses a fork of the standard syslog package to stream logs directly to state machine rsyslog daemon, without the need for a local rsyslog install.

The forked version of syslog allows TLS connections, and works from Windows.
Its a forked version of the standard syslog package. Works with syslog and rsyslog. Renamed it here because there is also:

github.com/juju/juju/utils/syslog

Getting imported a bit lower. We could rename that one, as it only takes care of generatin rsyslog configs.