security/tang: Update to v12

ChangeLog: https://github.com/latchset/tang/releases/tag/v12

• A few small changes for BSD support after standalone changes
• tang: allow running standalone
• When json_load_file fails report the error details information
• Fix service to include configured group
• Add documentation in service files

PR: 269573
Reported by: hdholm@alumni.iastate.edu (maintainer)