Add rel attribute to the Exit this Page button

[querkmachine]

Adds the rel="nofollow noreferrer" attribute to the Exit this Page button, so that the button:

• Does not unduly endorse the external webpage in search rankings.
• Does not provide a referrer header or information about the current browsing context to the external webpage, as this could be used by the target webpage to reveal information about the originating page.

Resolves #3921.

Changes

• Adds { 'rel': 'nofollow noreferrer' } the attributes parameter of the govukButton macro.
• Adds tests for the new default functionality.
• Adds changelog entry.
  • Also tweaks the wording of some of the other 'suggested change' entries.

[owenatgov]

One comment. Looking good.

I wonder if @claireashworth should sus out the changelog entry now or later. Claire, have you been reviewing other changelog entries for 5.0 before they get merged into main?

[colinrotherham]

One tiny minor thing

Although we often quote attributes keys like "data-attribute" so not a blocker

[owenatgov]

We're looking good. One final thing I forgot in my previous review: could we also update the child maintenance and ETP with skiplink examples so that the secondary links on those pages include the rel improvement?

[querkmachine]

@owenatgov It is done!

One of the skiplinks was missing any text, too. Fixed that while I was at it. Ooerr.

[owenatgov]

💪🏻