Add point cloud network support

[supersergiy]

Summary

• Add support for PointNet, PointNet++, and DGCNN architectures
• Wrap existing pointnet package for PointNet/PointNet++ models
• Implement DGCNN using torch_geometric's DynamicEdgeConv

Changes

• New zetta_utils/convnet/architecture/pointcloud.py module
• Add pointcloud optional dependency in pyproject.toml

[nkemnitz]

You'll have to include the pointcloud package to at least all for CI to pick it up (and update the requirements files).
... probably should even go into modules