Update `dvctable` style

To match https://github.com/iterative/dvc/pull/7142 (when merged)

• Alternating background color in rows
• Use rich box.HORIZONTALS style (https://rich.readthedocs.io/en/stable/appendix/box.html)

[julieg18]

Using prismjs, here is what I’ve been able to do so far:

The only thing I couldn’t figure out how to do was coloring the header cells. We can use regex and our already made dvctable methods to color the header text itself. But since the new design has no lines in between the header columns, there isn’t a way to figure out where a cell starts/stops with just regex. Though if we think this is good enough, we could merge this for a first iteration 🤔 cc @iterative/websites

[shcheklein]

Looks great @julieg18 ! I think we can go ahead and merge it like this.