pybind/rados: enable alternate types for key names

pybind/rados: enable alternate types for key names

Specifically, allow the caller to select the Python bytes type as an
acceptable key type.

This is important when the omap keys contain data that cannot be decoded
as a UTF-8 string. Encountering such a key currently stops the iteration
and makes the key virtually inaccessible by pyrados.

Fixes: https://tracker.ceph.com/issues/59716
Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>
(cherry picked from commit e796ea5c1489ad494dd28b68786a0dc25b62f9c3)