Feature request: pretrained checkpoints for dm-haiku models

[rdilip]

The current hk.nets module has a few different models. Would it be possible to open source basic checkpoints for these (in particular, the ResNet50V2 trained on ImageNet seems like it would be particularly useful for the community, but the others as well)? I know deepmind-research has a few, but making in part of the module import itself (in the style of Pytorch/tensorflow) or perhaps as an initializer would be quite useful.