Merge branch 'ps/refstorage-extension' into ps/worktree-refdb-initialization

* ps/refstorage-extension: t9500: write "extensions.refstorage" into config builtin/clone: introduce `--ref-format=` value flag builtin/init: introduce `--ref-format=` value flag builtin/rev-parse: introduce `--show-ref-format` flag t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar setup: introduce GIT_DEFAULT_REF_FORMAT envvar setup: introduce "extensions.refStorage" extension setup: set repository's formats on init setup: start tracking ref storage format refs: refactor logic to look up storage backends worktree: skip reading HEAD when repairing worktrees t: introduce DEFAULT_REPO_FORMAT prereq 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