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>