sdba Adjust methods work in adjust function

[coxipi]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• This PR does not seem to break the templates.
• CHANGELOG.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• dtrain in adjust is optional, you can instead pass a method str, to use a biasadjust method that only uses adjust

Does this PR introduce a breaking change?

Not for now. If we would like a more natural ordering or arguments in the adjust signature, then we would need some breaking changes (for now I've put the new arguments at the very end of the signature)

Other information:

• group needs to be passed in xclim_adjust_args when using this method. It can be the unparsed group. Is there a problem with this way of doing this? IMO, this is better than having to explicitly pass group to the function.
  I my YAML scripts, I directly put the group in xclim_train_args, and I know that those kwargs must be parsed at some point, e.g. because group comes from a YAML, is not yet a Grouper.

[RondeauG]

Is this PR still relevant? Is it ready for review? @coxipi