feat: Sanitize Markdown Inputs

[bliutech]

Currently, to display the generated Markdown, we are using dangerouslySetInnerHTML which has some complex implications for security. To be truly cautious, it would be nice to use DOMPurify to sanitize all contributed blog posts. isomorphic-dompurify is probably the best library to use due to server side rendering. https://github.com/kkomelin/isomorphic-dompurify There may need to be a bit of wrangling with the Next.js build configuration due to including this library. kkomelin/isomorphic-dompurify#54

[r2dev2]

We manually approve all markdown before merging. If one of our contributors wanted to be malicious (with 0 important cookies), they could just add a full html page.