Merge branch 'ps/clone-into-reftable-repository'

Merge branch 'ps/clone-into-reftable-repository'

"git clone" has been prepared to allow cloning a repository with
non-default hash function into a repository that uses the reftable
backend.

* ps/clone-into-reftable-repository:
  builtin/clone: create the refdb with the correct object format
  builtin/clone: skip reading HEAD when retrieving remote
  builtin/clone: set up sparse checkout later
  builtin/clone: fix bundle URIs with mismatching object formats
  remote-curl: rediscover repository when fetching refs
  setup: allow skipping creation of the refdb
  setup: extract function to create the refdb