Add comments section from YAML front matter

[gadenbuie]

The goal would be to put bluesky-comments.post in the YAML front-matter as a signal that a comments section should be added at the end of the post (with a header configurable by bluesky-comments.header:

---
title: My nifty blog post
bluesky-comments:
  post: https://bsky.app/profile/grrrck.xyz/post/3lg6fjlw2n225
---

or

---
title: My nifty blog post
bluesky-comments:
  post: 3lg6fjlw2n225
  profile: grrrck.xyz # could be set in _quarto.yml
  # profile: did:plc:72jpccg3u3vbohc67rqrplei
---