[Doc] Add <DataTable hiddenColumns> documentation

[Madeorsk]

Problem

We mention and link the prop hiddenColumns but we didn’t write anything about it.

Solution

Write a section of the DataTable on the hiddenColumns prop.

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• [ ] The PR includes unit tests (if not possible, describe why)
• [ ] The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

[fzaninotto]

please place this section in alphabetical order with other props.

[fzaninotto]

Suggested change

	Using the `hiddenColumns` property instead of removing `<DataTable.Col>` elements entirely allows hidden columns to be displayed again using a `ColumnsButton`, as in [Hiding or Reordering](#hiding-or-reordering-columns) section.
	Using the `hiddenColumns` instead of removing `<DataTable.Col>` elements allows hidden columns to be displayed again using a `<ColumnsButton>`, as explained in the [Hiding or Reordering Columns](#hiding-or-reordering-columns) section.

[fzaninotto]

I'd show the PostListActions with its ColumnsButton, otherwise the example falls short.

[Madeorsk]

I did it, but wouldn't it be better to keep this example minimal to only demonstrate the documented property?
I'd remove entirely, as the documentation about Hiding or Reordering Columns already documents this.

[fzaninotto]

I'd put this code snippet right after the first sentence, "by default..."