Rethink the way arguments are passed in `get_pairwise_comparisons()`

[nikosbosse]

As discussed in https://github.com/epiforecasts/scoringutils/pull/737, there are a few things that we could improve/make clearer related to the workflow of get_pairwise_comparisons().

In particular this concerns the way users can change the default test to apply for getting p-values (wilcoxon or permutation test) as well as the null hypothesis for the permutation test. Seb previously suggested the following:

Also given the prominence of the test type in the documentation perhaps make test_type an explicit argument rather than passing it via ellipsis?

[seabbs]

Also given the prominence of the test type in the documentation perhaps make test_type an explicit argument rather than passing it via ellipsis?

Agree