UI Link: Differentiate in the sidebar that this is an external link

[joepavitt]

Description

I've added a ui-ink to the sidebar, and it's not clear that it'll behave differently to the ui-page elements in the page navigation.

Whilst not all users will want this, we should at least provide an option to show an "external-link" icon or something to the right of the text to signify this will navigate away from the Dashboard.

Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate