[Script request] Hexo 渲染的文章不支持 plantuml 需要适配

**Theme Branch**: All

我们采用的编辑器 Vditor 支持 plantuml 渲染。如果在编辑器中输入一个 plantuml 代码块，就可以实时渲染出 uml 图片。
但是发布后在模板中是不支持这样渲染的，只会被当作纯代码块。


**Describe the solution you'd like**
请研究一下如何在 markdown-it 中渲染出 plantuml 的代码块，比如尝试使用 npm 包 [markdown-it-plantuml](https://www.npmjs.com/package/markdown-it-plantuml)。

**Additional context**: Add any other context about the theme here.

Start at the theme's markdown-it rendering entry point and compare its handling of published code blocks with Vditor's PlantUML behavior. Evaluate the suggested markdown-it-plantuml npm package; done means PlantUML blocks render as UML images in published Hexo articles rather than plain code.

Written by the indexing model from the issue text.