devel/git-filter-repo: New port - a versatile tool for rewriting history

git filter-repo is a versatile tool for rewriting history, which
includes capabilities I have not found anywhere else. It roughly falls
into the same space of tool as git filter-branch but without the
capitulation-inducing poor performance, with far more capabilities, and
with a design that scales usability-wise beyond trivial rewriting cases.
git filter-repo is now recommended by the git project instead of
git filter-branch.