Add LZ4 as a default requirement

@shughes-uk suggested that we might include LZ4 by default as a dask requiement. It's lightweight and sometimes creates issues

One solution would be to modify the metapackage:

https://github.com/conda-forge/dask-feedstock/blob/main/recipe/meta.yaml

Although I think that right now we've actually handled this in the handshake. dask servers are robust to only some nodes having lz4.