[DataTableSkeleton] Add prop to hide header in table skeleton

Summary

After #5752 was merged, the DataTableSkeleton component always has a header now, which is a change from how it used to look previously (which is understandable, given the v10 bump).

For the React component, it would be nice to have a prop such as showHeader that can show or hide the extra divs, instead of having to apply some sort of CSS to hide them.

[richardpilot]

There are also use cases where you want the DataTable to be a skeleton but you have actions available in the toolbar that do not need a skeleton. For example, the primary button of a table being create new object, which can still occur whilst the underlying data is being refresh (causing a skeleton) e.g.

[asudoh]

@nictownsend My apologies for the change in table skeleton yielded a minor breaking change; The change was meant to be part of v10 but the team slipped it through the crack, and it was seen not worth waiting for v11. A possible future consideration for this area is better release noting.

Wrt providing an option to hide title/description portion, technically it makes sense, but let’s see what @carbon-design-system/design thinks from the point of whether our design guide since v10 allows it.