[COOK-3608] Split `mail.*` facilities

The split mail.* facilities in the `50-default.conf` template is a problem for me on mail servers.  This seems to be an opinionated addition to Debian-ish rsyslog defaults as shipped, however I retained that functionality on non-RHEL systems for cookbook backwards compatibility.

The `50-default.conf` is very much geared towards Ubuntu/Debian. Which is not a huge problem, but the cookbook generates log files which will never get rotated on RHEL family, and probably other, systems.

This adds a hash knob to allow log facilities and log destination to be rendered in the `50-default.conf` template for these two requirements.

Signed-off-by: Seth Vargo <sethvargo@gmail.com>