docs: Fix URL formatting in deprecation warnings (#23075)
**Description**
Updated the URLs in deprecation warning messages. The URLs were
previously written as raw strings and are now formatted to be clickable
HTML links.
Example of a broken link in the current API Reference:
https://api.python.langchain.com/en/latest/chains/langchain.chains.openai_functions.extraction.create_extraction_chain_pydantic.html
<img width="942" alt="Screenshot 2024-06-18 at 13 21 07"
src="https://github.com/langchain-ai/langchain/assets/4854600/a1b1863c-cd03-4af2-a9bc-70375407fb00">
