Update links to workhorse files

The following discussion from !84115 (merged) should be addressed:

• @aqualls started a discussion:

  Investigate in the www-gitlab-com repo:

  ./sites/handbook/source/handbook/engineering/development/dev/gitaly/index.html.md.erb:
  ./sites/uncategorized/source/blog/blog-posts/2021-11-18-deep-dive-tech-stack-behind-spamcheck.html.md.erb

• Also, I'll need to add these pages to the left nav.