Related footer

[mmontesanonyc]

PR checklist:

• [x] Changes previewed and QC'ed
• [x] In PR, mention team member for FYI, review, or approval

New content (if applicable):

• [ ] Date updated
• [ ] Tags and keywords updated
• [ ] Feature box updated

New data (if applicable)

• [ ] Added to Recently Updated
• [ ] Added to 311-crosswalk

[mmontesanonyc]

Opening this PR but don't want to merge it just yet - @etorem let's touch base on applying these changes more broadly:

• reviewing where the related-footer-2 partial is used (and tidying up old partials)
• adding more related content to other content types' frontmatter
• Thinking through what we want to do for the data explorer