docs: Add conditional js/python rendering (#5128)

# Overview

Adding conditional rendering logic to co-locate js and python documentation.

* `:::` conditional syntax can be used to switch between python only or js only content.
* Contains simple unit tests for `:::`
* PR adds set up for a way to implement a context switch between languages, but it will not be enabled until JS content is merged in.
* Contains a script that can add javascript documentation 

Implementation of: https://github.com/langchain-ai/langgraph/pull/5118

## Example

Example of conditional rendering / compilation.


```markdown

### Config (static context)

Config is for immutable data like user metadata or API keys. Use
when you have values that don't change mid-run.

Specify configuration using a key called **"configurable"** which is reserved
for this purpose:


:::python

This content will only be rendered for the python site.
:::

:::js
this content will only be rendered for the js / ts site.
:::

```

docs/_scripts/link_map.py

@@ -0,0 +1,5 @@
+JS_LINK_MAP = {
+    "langgraph.types.interrupt": "https://langchain-ai.github.io/langgraphjs/reference/functions/langgraph.interrupt-2.html",
+    "create_react_agent": "https://langchain-ai.github.io/langgraphjs/reference/functions/langgraph_prebuilt.createReactAgent.html",
+    "langgraph.types.Command": "https://langchain-ai.github.io/langgraphjs/reference/classes/langgraph.Command.html",
+}