periodic: Make daily diff(1) flags configurable with daily_diff_flags
PR: 270266
Approved by: jrm (mentor), karels
MFC after: 1 month
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D42900
(cherry picked from commit 15e35d058cff847d1a7bc671fcf48b99f5d2f73b)