sysutils/dust: Update to 0.8.6 and take maintainership

Also: add manpage, completion files, and sample config. Rewrite
pkg-descr to say what it actually does. And, take maintainership
after multiple maintainer timeouts (the last we've heard from
the outgoing maintainer was when they filed a PR to take
maintainership).

PR: 271268
Approved by: maintainer timeout