Merge branch 'kn/refs-generic-helpers' into seen

Merge branch 'kn/refs-generic-helpers' into seen

Refactor service routines in the ref subsystem backends.

* kn/refs-generic-helpers:
  refs: use peeled tag values in reference backends
  refs: add peeled object ID to the `ref_update` struct
  refs: move object parsing to the generic layer
  update-ref: handle rejections while adding updates
  update-ref: move `print_rejected_refs()` up
  refs: return `ref_transaction_error` from `ref_transaction_update()`
  refs: extract out reflog config to generic layer
  refs: introduce `ref_store_init_options`
  refs: remove unused typedef 'ref_transaction_commit_fn'