Consolidating the hooks to avoid duplication of logic
We need this change for consolidating js and python content: we need include-markdown to run as a mkdocs plugin before our pipeline (rather than as markdown extension which runs after our hooks plugin).
* Expand chat model documentation a bit.
* Adds links to langchain docs to make relevant information easier to find.
* This is a stop-gap until we merge langchain and langgraph docs
Manual pass to apply a few heuristics:
* Boost conceptual pages
* Deboost (is that a word?) index pages that list all content
* Prefer Agents pages if search query contains the word "agent"
* Add tags for a few selected pages
