Ensure types are displayed in documentation

[omad]

I think that they are, but there could be conflicts between PyDoc types and Type Annotation types, and we should make sure they're both consistent, and that we're displaying the Type Annotation types. They're automatically checked and are almost certain to be accurate.

It's apparently sphinx-autodoc-typehints that does that, and it's present in docs/requirements.txt, so I can look into enabling that.

It doesn't look too hard to convert the PyDoc to type annotations, so I can look into that too.

Originally posted by @pjonsson in https://github.com/opendatacube/datacube-core/pull/1760#discussion_r2074869610