lesspipe: Allow zstd to operate on a symlink

By default zstd refuses to operate on symlinks, so for example
zless /var/crash/vmcore.last.zst failed to view the uncompressed core
file. Add -f to the zstd command line to allow operation on symlinks.

Reviewed by: delphij
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D55101

(cherry picked from commit b4305c90a3be7e1a40b76545b8b761fdbda5c309)
(cherry picked from commit 68125692efacbce537e14ba16ecedff750cccc36)