Rename/reword `parallel=True` option to `open_mfdataset`

What is your issue?

Based on its name, I was surprised to find that open_mfdataset(..., parallel=True) computed the whole dataset eagerly, whereas parallel=False just returned it in dask form. (I generally think of "dask" as related to "parallel".)

I guess the docs do technically say this, but it's a bit hard to parse:

If True, the open and preprocess steps of this function will be performed in parallel using dask.delayed. Default is False.

The docstring could maybe instead mention "If False (default), the data is returned in dask form. If True, it will be computed immediately (using dask), then returned in NumPy form".

More intuitive to me would be renaming the argument to compute=False. Or even deprecating the argument entirely and having a load_mfdataset function, in the same way that load_dataset is the eager version of open_dataset.

Start with the open_mfdataset entry point and its generated documentation, especially the description of the parallel option. Review the existing behavior and related open_dataset/load_dataset API before deciding whether the issue calls for wording, a renamed option, or a new function. Done means the chosen API or documentation clearly distinguishes lazy and eager behavior, with coverage for the resulting interface.