docs: Outline Jsonnet language (#19410)

This PR adds a basic documentation about the Jsonnet language support.

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

docs/src/languages.md

@@ -32,6 +32,7 @@ Zed supports hundreds of programming languages and text formats. Some work out-o
 - [JavaScript](./languages/javascript.md)
 - [Julia](./languages/julia.md)
 - [JSON](./languages/json.md)
+- [Jsonnet](./languages/jsonnet.md)
 - [Kotlin](./languages/kotlin.md)
 - [Lua](./languages/lua.md)
 - [Luau](./languages/luau.md)
@@ -104,7 +105,6 @@ Zed supports hundreds of programming languages and text formats. Some work out-o
 - [Groq](https://github.com/juice49/zed-groq)
 - [INI](https://github.com/bajrangCoder/zed-ini)
 - [Java](https://github.com/zed-extensions/java)
-- [Jsonnet](https://github.com/narqo/zed-jsonnet)
 - [Justfiles](https://github.com/jackTabsCode/zed-just)
 - [LaTeX](https://github.com/rzukic/zed-latex)
 - [Ledger](https://github.com/mrkstwrt/zed-ledger)