[FEA] Support Graph Creation for Graph Databases

[alexbarghi-nv]

We currently do not have an effective way to build a homogeneous or heterogeneous graph from graph database data (i.e. a set of files with non-contiguous vertex and edge ids labeled by vertex and edge type). We should create a means of doing this using PyTorch/NCCL and add appropriate examples. In the long term, it might make sense to contribute this to upstream PyG.

We should also provide a function that handles when there is an imbalance of labeled data across ranks by evening out the label distribution through shuffling.