Merge branch 'ds/midx-expire-repack'

Merge branch 'ds/midx-expire-repack'

"git multi-pack-index" learned expire and repack subcommands.

* ds/midx-expire-repack:
  t5319: use 'test-tool path-utils' instead of 'ls -l'
  t5319-multi-pack-index.sh: test batch size zero
  midx: add test that 'expire' respects .keep files
  multi-pack-index: test expire while adding packs
  midx: implement midx_repack()
  multi-pack-index: prepare 'repack' subcommand
  multi-pack-index: implement 'expire' subcommand
  midx: refactor permutation logic and pack sorting
  midx: simplify computation of pack name lengths
  multi-pack-index: prepare for 'expire' subcommand
  Docs: rearrange subcommands for multi-pack-index
  repack: refactor pack deletion for future use