tools: Add clear-data-digest command to objectstore tool.

tools: Add clear-data-digest command to objectstore tool.

There may be a situation where data digest in object info is
inconsistent with that computed from object data, then deep-scrub
will fail even though all three repicas have the same object data.

Fixes: https://tracker.ceph.com/issues/37935
Signed-off-by: Li Yichao <liyichao.good@gmail.com>
(cherry picked from commit da5832b2b49be4ab23f7ffc5ba1ba630168b886f)

Conflicts:
    src/tools/ceph_objectstore_tool.cc
- change cbegin() to begin() to get it to build