Align with kval

[oyvfoss]

Currently, kobbe is built as a self-standing library. We want to make it dependent on kval. These modules are intended to be part of the same ecosystem, and we want to be able to use base functionality from kval in kobbe.

Examples of functionality from kval can be:

• Functions for modyifing metadata, dropping variables etc.
• Functions for CF-formatting and export.

Most of these will probably be wrappers for xarray functionality, with NPIOcean ecosystem conventions on top.

This will presumably all be significantly easier once we have kval on pypi.

[oyvfoss]

Some of this is implemented. Closing because this is too vague to be useful.