make related articles easier to maintain

[jbolda]

We currently use a custom html component in our markdown blog post files to curate content for the users. This is difficult to maintain as our styles are baked into the blog posts, and the content (title, description, etc.) are duplicated.

https://github.com/thefrontside/frontside.com/blob/1d51d53a375cb0d46d057067cbd7df60303cb920/src/pages/blog/2021-18-02-there-and-back-again-testing-and-upgrades.md#related-article

We can instead put a reference to a page slug in the blog post frontmatter, and using that, pull the related data out of the graph.