rgw: radosgw-admin errors if marker not specified on data/mdlog trim

rgw: radosgw-admin errors if marker not specified on data/mdlog trim

Check that a marker was specified and trim if we don't have one.

Also: In a world where we're parsing for generation, it doesn't really
make sense to have a 'no marker specified' as separate from a marker
that is just an empty string.

Also: Successful datalog trim returns zero, not
-ENODATA, and radosgw-admin should expect this.

Fixes: https://tracker.ceph.com/issues/51712
Signed-off-by: Adam C. Emerson <aemerson@redhat.com>