Add Nofollow-Dofollow Link checker

[alisha-kamat]

Summary of Changes

• Add Outgoing Nofollow-Dofollow Link Checker under the SEO tab under Article Edit Section
• The new feature will allow the admin to monitor the external links of the article and categorize them as dofollow and nofollow
• It will enable developers to prevent ‘link juice’ from flowing out to unwanted sites based on the external site's credibility
• Admins can choose to retain or change the ‘rel’ directive (from dofollow to nofollow or vice versa) by going to the 'Content' tab on the same page

Testing Instructions

• Go to the 'Content' tab under Article Edit Section
• Click on 'Toggle Editor' and add a few anchor tags to the article
• Change some of the 'rel' attributes of these tags to nofollow
• Now move over to the 'SEO' tab and take a look at the Outgoing Link Checker section
• A list of all the outgoing nofollow and dofollow links will appear

Actual result BEFORE applying this Pull Request

• The Outgoing Nofollow-Dofollow Link Checker section should not be present under the SEO tab

Expected result AFTER applying this Pull Request

• The newly added Outgoing Nofollow-Dofollow Link Checker section should be visible

[uglyeoin]

It would be good to have a default option for external links e.g. no-follow. I'm not sure how feasible this is, and it wouldn't need to be for all links, but it would be good to have it as the default. If we are doing that, it might also be nice to have a default icon or something similar for external links. I do note that the UK Gov website, which I see as leading in terms of accessibility, follows a new process of writing (external link) instead of using an icon.