Merge branch 'ps/ref-storage-migration' into ps/use-the-repository

* ps/ref-storage-migration: builtin/refs: new command to migrate ref storage formats refs: implement logic to migrate between ref storage formats refs: implement removal of ref storages worktree: don't store main worktree twice reftable: inline `merged_table_release()` refs/files: fix NULL pointer deref when releasing ref store refs/files: extract function to iterate through root refs refs/files: refactor `add_pseudoref_and_head_entries()` refs: allow to skip creation of reflog entries refs: pass storage format to `ref_store_init()` explicitly refs: convert ref storage format to an enum setup: unset ref storage when reinitializing repository version