deprecate **kwargs in most methods?

[gdementen]

In order to tighten the api, I would like to list all methods taking **kwargs and examine if we could deprecate that syntax for most cases.

For example, what's left of #1120 is only present for **kwargs and I wonder if accepting only ("old_key", "new_key") and (dict_of_changes) in reindex, set_labels, rename, set_axes, etc. wouldn't be a good idea but this needs to be decided with the whole API in mind, which I don't want to do now.

One case I would regret if we deprecate everywhere is Session(arr1=arr1) but let's see the full picture before deciding 🤷‍♂️ .