textproc/groff: Update 1.23.0 => 1.24.0, take maintainership

• Clarify LICENSE
• Add LICENSE_FILE
• Add DOCS and EXAMPLES options
• Switch from custom to canonical EXAMPLESDIR
• Pet portclippy(1) and portfmt(1)

Reviewed by: vvd@
Approved by: yuri@ (Mentor)
Approved by: db@, yuri@ (Mentors, implicit)
Differential Revision: https://reviews.freebsd.org/D55637