add dask kwargs

[bolliger32]

• [x] tests added / passed
  • [x] docs reflect changes
  • [ ] passes flake8 rhg_compute_tools tests docs
  • [x] entry in HISTORY.rst

Add the ability to pass kwargs to client.submit and client.gather as part of the rhg_compute_tools.xarray functions. I came across a situation where I wanted to pass the priority kwarg, so figured we might as well add the ability to pass any arbitrary kwarg here.

[bolliger32]

Feels very general using a name like dask_kwargs? Dask does lots of stuff... Considering dask_client_kwargs or something like mapgather_kwargs as alternatives? I'm thinking of a future case where you need another kwarg passing to something else for dask. Calling this addition dask_kwargs might be too general?

I like it - changed to just client_kwargs.