feat: add skip load and save option

[yoshinorin]

What is this?

I submitted #123 PR for huge posts.
However sometimes hexo is no need to load from db.json. Also save to db.json.

e.g: Execute hexo g in GitHub Actions.

This PR purpose is to add an option for ignore them.

[SukkaW]

If we don't need to save db.json, just do it in Hexo. In Hexo there is a hexo.database.load() method and a this.database.save() method. We should add the skip loading and saving there instead.

[yoshinorin]

Thank you :)