Merge branch 'cc/repack-sift-filtered-objects-to-separate-pack'

"git repack" machinery learns to pay attention to the "--filter=" option. * cc/repack-sift-filtered-objects-to-separate-pack: gc: add `gc.repackFilterTo` config option repack: implement `--filter-to` for storing filtered out objects gc: add `gc.repackFilter` config option repack: add `--filter=<filter-spec>` option pack-bitmap-write: rebuild using new bitmap when remapping repack: refactor finding pack prefix repack: refactor finishing pack-objects command t/helper: add 'find-pack' test-tool pack-objects: allow `--filter` without `--stdout`