Log pfsense version to syslog after bootup

This will log a syslog entry after bootup that has the pfsense version (arch, platform, etc).  This can come in handy for admin purposes to be able to view the logs on a remote server to see what version of pfsense was running at what time.  This can come in handy when you are changing versions a lot and need to know what version you were running a few days ago at a specific time.

The current syslog entries are not very helpful for this.  /var/log/dmesg.boot does have the kernel version logged but it is overwritten on each boot and only resides on the firewall itself which can not serve the purpose of a history.  The kernel version does not get sent to remote syslog servers because networking, etc isn't up soon enough.

Discussion about it:
https://forum.pfsense.org/index.php?topic=77713.0