periodic: add support for .xz and .zcat compressed logs

Also improve temporary file usage in 200.accounting, add an xref to
zstd(1) to newsyslog.conf.5, and clarify in periodic.conf that
"daily accounting" means process accounting and "monthly accounting"
is login accounting.

PR: 253868
Reviewed by: allanjude
Approved by: blackend (mentor)
Differential Revision: https://reviews.freebsd.org/D29267