MINOR: map/acl: add the "prepare map/acl" CLI command

This command allocates a new version for the map/acl, that will be usable
later to prepare the addition of new values to atomically replace existing
ones. Technically speaking the operation consists in atomically incrementing
the next version. There's no "undo" operation here, if a version is not
committed, it will automatically be trashed when committing a newer version.
2 files changed