sysutils/restic: Update to 0.8.1, add options, new maintainer

• Install man pages
• Add options for bash and zsh completions

Upstream changes: https://github.com/restic/restic/releases

PR: 224806
Submitted by: gregf@hugops.pw (new maintainer)
Approved by: wg@FreeBSD.org (old maintainer)
Differential Revision: https://reviews.freebsd.org/D13722