Merge branch 'gc/use-repo-settings'

It is wrong to read some settings directly from the config
subsystem, as things like feature.experimental can affect their
default values.

* gc/use-repo-settings:
  gc: perform incremental repack when implictly enabled
  fsck: verify multi-pack-index when implictly enabled
  fsck: verify commit graph when implicitly enabled

diff --cc builtin/fsck.c
Simple merge

diff --cc t/t5319-multi-pack-index.sh
Simple merge