Store category slugs in the article_slug_versions table

[jacqui]

Trying to prevent broken links when a category slug is changed but links to articles are published already using the old category slug:

I think adding the category slug on every change to the existing article_slug_versions table could work.

• [x] (hasura) It would mean adding a category_slug column to the table
• [x] (hasura) backfill existing article + category combinations into the article_slug_versions table in a sql migration
• [x] Update the storeArticleIdAndSlug function to store the category slug plus article id & article slug
• [x] Update calls to the function on article save: publish and preview
• [x] (frontend) change the graphql lookup on article_slug_versions to include category_slug in the primary where clause