[Optimization-wholegraph] Remove CUDA dependency during conversion to WholeGraph format

Node features are transformed from DGL format to WholeGraph format using the [convert_feat_to_wholegraph.py](https://github.com/awslabs/graphstorm/tree/main/tools) script. However, this script significantly consumes memory, prompting us to explore utilizing our substantial CPU instances like `r5` or `X1`. Unfortunately, due to its reliance on WholeGraph's CUDA dependency (pylibwholegraph.binding.wholememory_binding), leveraging these instances is currently not possible. Are there alternative approaches to address this limitation?