Add support for menu item grouping

[ecircenis]

Can we get support for menu item grouping in Designer, as shown in the second example here?
https://design-system.hpe.design/components/menu?q=menu#grouping

A design idea to consider: if I add a menu item of "-", it is interpreted as a separator and any link for that item is ignored.

[ericsoderberghp]

This is now available.