Allow to define borders for table th/td

[lcarcone]

Some pages we want to redesign have survey results displayed in tables.

Some of these tables can have many columns and are easier to read if each column is separated (especially if there are many responses)

Such tables can be seen at https://w3c.github.io/wbs-design/html/s24-qtypes-results.html#xq13 or https://w3c.github.io/wbs-design/html/s24-qtypes-results.html#xq15 for instance.

For this results page, I added the local css rule
td, th {
border-right: solid 1px #bdbdbd;
}

Can a similar rule be added in the Design System so that it can be selected if needed ?