Automate makeOutboundLink `rel` attribute handling

[afercia]

In MyYoast, see https://github.com/Yoast/my-yoast/pull/2279, we've made the Link component able to automatically handle the rel attribute.

As per https://github.com/Yoast/wordpress-seo/issues/4605#issuecomment-425409923, the desired behavior is:

• use noopener for all the non-yoast.com external links
• omit it for the yoast.com links (including shortened links)

In WordPress, noreferrer is redundant, especially after https://core.trac.wordpress.org/changeset/41741 see https://core.trac.wordpress.org/ticket/42036

Currently, each time we don't want a rel attribute rendered, we're explicitly passing a rel={ null }. This is prone to human errors and can be easily forgotten. makeOutboundLink should handle this automatically.

[hwinne]

12262 (Free) still needs action, 2259 (Premium) CR Done 👍 , 9 (Monorepo) CR Done 👍

[afercia]

Moving to code review done as the previous PR was already CR'ed.