WS-2573: Article removal from UAS if article does not exist anymore

[jinidev]

Resolves JIRA:
https://bbc.atlassian.net/browse/WS-2573
https://bbc.atlassian.net/browse/WS-2936

Summary

When a logged-in user visits a saved article, but that article does not exist anymore, on the World Service website, the system should check whether that article already exists in UAS (User Activity Service) as a saved article.

If the article is saved:
Remove the article from UAS if the article no longer exists

Code changes

• List key code changes that have been made.

Testing

1. Save an article using the following URL (example): http://localhost.bbc.com:7081/hindi/articles/cn4rzp8zlxyo?renderer_env=live
2. Navigate to the My News page: http://localhost.bbc.com:7081/hindi/my-news
3. Open the previously saved article without the renderer_env=live parameter (this should result in a 404 page).
4. Verify that the article is automatically removed from the User Activity Service (UAS) and no longer appears in the saved articles list.

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