Support for custom media directory

See attached plugin im using https://www.dropbox.com/scl/fi/ylinrh235j6sfo4ugknoz/custom-media-directory-5.0.1.zip?rlkey=03l6aqcbtt4cqlbco33etdhe1&st=fsxcvfds&dl=0

AMO’s get_attachment_subdir() was written assuming the local upload structure is always either the WordPress default (YYYY/MM/) or flat (no subdirectory). It has no awareness of custom directory prefixes injected by upload_dir filters like CMD’s. The fix would belong in AMO — it should derive the cloud subdirectory directly from _wp_attached_file post meta (which always contains the correct relative path that CMD sets), rather than re-parsing the file path with a numeric year/month assumption.