Configure periodic tasks on FreeBSD

Summary:
FreeBSD offers a periodic system to run tasks,
most enabled by default, some to configure.

This change enables the following behavior:

• update daily ports tree
• resync NTP clock
• run ZFS scrub every 5 weeks

Reference: man 5 periodic.conf

Ref T1541 for zfs part.

Test Plan: Configuration extracted from Ysul, to test on WindRiver

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1541

Differential Revision: https://devcentral.nasqueron.org/D2203