support customized dataLoaders?

[ifiaposto]

DataLoaderAdapter, and as a result DataLoaderShard returned by prepare, sets:

self.base_dataloader = DataLoader(dataset, batch_sampler=batch_sampler, **kwargs)

I think it would be very useful if prepare_dataloader passed the type of the original dataloader when creating the DataLoaderShard and extend DataloaderShard to support customized dataloader types. Otherwise, the functionality seems very limited.