Merge branch 'ab/commit-graph-progress'

Merge branch 'ab/commit-graph-progress'

Generation of (experimental) commit-graph files have so far been
fairly silent, even though it takes noticeable amount of time in a
meaningfully large repository.  The users will now see progress
output.

* ab/commit-graph-progress:
  gc: fix regression in 7b0f229222 impacting --quiet
  commit-graph verify: add progress output
  commit-graph write: add progress output