Touch up hover tools

[ahuang11]

From Maxime in #1385

I've got a few comments.

Doesn't hover_mode duplicate what is already possible with setting hover to e.g. 'vline'? This was added in https://github.com/holoviz/hvplot/pull/493 but never documented I believe.

Don't think a test is required since it's just adding plot_opts?

Adding tests is pretty much always worth in my opinion, in particular when they're easy to write.

I would suggest alphabetically ordering the new hover_* parameters in the signature, docstring, and doc.

We need to find a way to better document these sorts of options. As it stands, I don't think the docs provide sufficient information for users to leverage these new parameters.

[maximlt]

Doesn't hover_mode duplicate what is already possible with setting hover to e.g. 'vline'? This was added in #493 but never documented I believe.

Oh this was not just a docs request, I think we have effectively duplicated the API.