Merge branch 'ps/pack-refs-auto'

"git pack-refs" learned the "--auto" option, which is a useful
addition to be triggered from "git gc --auto".

Acked-by: Karthik Nayak <karthik.188@gmail.com>
cf. <CAOLa=ZRAEA7rSUoYL0h-2qfEELdbPHbeGpgBJRqesyhHi9Q6WQ@mail.gmail.com>

* ps/pack-refs-auto:
  builtin/gc: pack refs when using `git maintenance run --auto`
  builtin/gc: forward git-gc(1)'s `--auto` flag when packing refs
  t6500: extract objects with "17" prefix
  builtin/gc: move `struct maintenance_run_opts`
  builtin/pack-refs: introduce new "--auto" flag
  builtin/pack-refs: release allocated memory
  refs/reftable: expose auto compaction via new flag
  refs: remove `PACK_REFS_ALL` flag
  refs: move `struct pack_refs_opts` to where it's used
  t/helper: drop pack-refs wrapper
  refs/reftable: print errors on compaction failure
  reftable/stack: gracefully handle failed auto-compaction due to locks
  reftable/stack: use error codes when locking fails during compaction
  reftable/error: discern locked/outdated errors
  reftable/stack: fix error handling in `reftable_stack_init_addition()`

diff --cc builtin/gc.c
Simple merge

diff --cc refs/reftable-backend.c
Simple merge

diff --cc reftable/stack_test.c
Simple merge