Add annotation in produced HTML for the language used

[pomber]

Discussed in #238

^{Originally posted by colelawrence July 26, 2022}
I am building a docs site with contentful and I would like to be able to see what language was actually used to produce the React .ch-code-scroll-parent element. Something like a data-ch-language="ts" would be extraordinary for my use-case, where I need to be able to read code blocks off of my own page coming out of the MDX content, so I can insert their source code contents into a demo iframe.

Thanks!

[github-actions]

🚀 Issue was released in v0.7.3 🚀