Add support for Jsonnet to Pygments

[davidzchen]

It would be nice to add Jsonnet highlighting to Pygments so that we can have syntax highlighting for Jsonnet code in Markdown fenced code blocks in static site generators such as Jekyll, which is also used for GitHub pages:

```jsonnet
{
  local Foo = {
    bar: "Some jsonnet code here"
  },
  baz: Foo {
    bar: "nicely syntax highlighted"
  }
}
```

[mikedanese]

Also adding a "grammar" to https://github.com/github/linguist would give syntax highlighting in github file view.

[davidzchen]

#23 tracks adding Jsonnet support to Linguist, and we sent a pull request github-linguist/linguist#2653, but at the time, there were not enough Jsonnet files in GitHub repositories.

Perhaps we should revisit that PR in the near future.

[sh0rez]

github-linguist/linguist#4455 has been merged nearly a year ago, I guess we can close this!

[sbarzowski]

@sh0rez Github support is there, but AFAICT we don't have support in Pygments (see: https://pygments.org/languages/).

[sh0rez]

Oh right, this was about Pygments as well. Ignore me 🤪

[bgagnon]

Jsonnet is supported by Rouge (demo: http://rouge.jneen.net/v3.19.0/jsonnet/) and there are IDE-specific implementations for VSCode, Jetbrains and Atom. But no Pygments :(

Personally, I'd like to have this for Mkdocs.

[AndrewEckart]

This was completed in pygments/pygments#2239

The change was released in Pygments version 2.14: https://pygments.org/docs/changelog/#version-2-14-0