[Model Request] Graph Matching Network

## 🚀 Feature
[Graph Matching Networks for Learning the Similarity of Graph Structured Objects](https://proceedings.mlr.press/v97/li19d/li19d.pdf)

There is model available in DGL that can do similarity learning for graph structured objects. But this has many important real world applications.

Is there a plan to add this model? Also, is there an alternative model that I can use as a stop gap?