Support for utterances and giscus

[beiyuouo]

PR Checklist

• The commit message follows guidelines for NexT.
• Tests for the changes was maked (for bug fixes / features).
  • Muse | Mist have been tested.
  • Pisces | Gemini have been tested.
• Docs in NexT website have been added / updated (for features).

PR Type

• Bugfix.
• Feature.
• Code style update (formatting, local variables).
• Refactoring (no functional changes, no api changes).
• Build & CI related changes.
• Documentation.
• Translation.
• Other... Please describe:

What is the current behavior?

Issue resolved: N/A

What is the new behavior?

• Screenshots with this changes:
  

• Link to demo site with this changes: https://blog-hexo.bj-yan.top/TODOLIST/

How to use?

In NexT _config.yml:

# Demo: https://utteranc.es/
utterances:
  enable: false
  repo: # Repository to store issues E.g. theme-next/blog-comments
  pathname: pathname # Issue title
  # theme: github-light | github-dark | github-dark-orange | icy-dark | photon-dark | dark-blue | boxy-light
  theme: boxy-light
  cdn: https://utteranc.es/client.js # No need to change

# Demo: https://giscus.app/
giscus:
  enable: false
  repo: # Repository to store issues E.g. theme-next/blog-comments
  repo_id: # Generated from giscus
  category: General # Github Discussion Category
  category_id: # Generated from giscus
  pathname: pathname # Discuss title
  reactions_enabled: 1
  emit_metadata: 0
  # theme: light | dark | dark_dimmed | dark_high_contrast | dark_protanopia | light_protanopia | transparent_dark | preferred_color_scheme
  theme: dark_dimmed
  cdn: https://giscus.app/client.js

[welcome]

Thanks so much for opening your first PR here!

[CLAassistant]

All committers have signed the CLA.