[Feature] add Waline comment system support

[lizheming]

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).
• Documentation.
• Translation.
• Other... Please describe:

What is the current behavior?

Issue resolved: N/A

What is the new behavior?

• Link to demo site with this changes:
• Screenshots with this changes:

How to use?

In NexT _config.yml:

# Waline. 
# You need deploy waline server in vercel then you can get serverURL
# more info please open https://waline.js.org
valine:
  enable: true
  serverURL: # Your waline server URL

[welcome]

Thanks so much for opening your first PR here!

[CLAassistant]

All committers have signed the CLA.

[stevenjoezhang]

Thanks for your contribution. Unfortunately, we cannot accept any comment systems related to Leancloud or Valine until we have thoroughly investigated the attack against Valine that occurred a few days ago. Ensuring user data security and privacy protection is our consistent pursuit, and we are planning to remove Valine in the next version. Maybe you can make your comment system into a third-party plug-in like this: https://github.com/next-theme/hexo-next-valine
And submit a pull request here: https://github.com/next-theme/awesome-next#comment

[lizheming]

OK, thank you for your reply. Although Waline is derived from Valine, it is much safer than Valine. Waline uses a variety of methods to forbidden spam, including akismet, post frequency base on IP, IP blackList, forbidden word detection and duplicate word detection. Base on those reasons, I hope you can consider again to support waline, thank you.