Regrid's weights location as kwarg

[aulemahal]

Pull Request Checklist:

• [x] pre-commit hooks are installed/active in my local clone ($ pre-commit install)
• [ ] This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
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What kind of change does this PR introduce?

• In regrid_dataset, moves weights_location to the keyword argument section.

Does this PR introduce a breaking change?

Yes, script using positional arguments for this function will break.

Other information:

As a kwarg it can be included in the config, but I may have missed something?

[RondeauG]

Does that still mean that the argument is required? If not, we have to account for cases where is is None.

[aulemahal]

It is still needed, but has to be given as a keyword. In fact, my problem was that I wanted to give it in the config, while giving the datasets positionally. We could also move weights_location before the ,*, and it would then be giveable both ways.

[RondeauG]

I'd go with before the *, then.