devel/jujutsu: Add new port

Jujutsu is a version control system that abstracts the user interface
from and version control algorithms from the storage systems used to
serve your content.

This allows it to serve as a VCS with many possible physical backends,
that may have their own data or networking models—like Mercurial or
Breezy, or hybrid systems like Google's cloud-based design, Piper/CitC.

This version of jujutsu supports Git repositories and its native
storage backend.