community: adding langchain-predictionguard partner package documentation (#28832)

- *[x] **PR title**: "community: adding langchain-predictionguard
partner package documentation"

- *[x] **PR message**:
- **Description:** This PR adds documentation for the
langchain-predictionguard package to main langchain repo, along with
deprecating current Prediction Guard LLMs package. The LLMs package was
previously broken, so I also updated it one final time to allow it to
continue working from this point onward. . This enables users to chat
with LLMs through the Prediction Guard ecosystem.
    - **Package Links**: 
        -  [PyPI](https://pypi.org/project/langchain-predictionguard/)
- [Github
Repo](https://www.github.com/predictionguard/langchain-predictionguard)
    - **Issue:** None
    - **Dependencies:** None
- **Twitter handle:** [@predictionguard](https://x.com/predictionguard)

- *[x] **Add tests and docs**: All docs have been added for the partner
package, and the current LLMs package test was updated to reflect
changes.


- *[x] **Lint and test**: Linting tests are all passing.

---------

Co-authored-by: ccurme <chester.curme@gmail.com>

libs/community/scripts/check_pydantic.sh

@@ -20,7 +20,7 @@ count=$(git grep -E '(@root_validator)|(@validator)|(@field_validator)|(@pre_ini
 # PRs that increase the current count will not be accepted.
 # PRs that decrease update the code in the repository
 # and allow decreasing the count of are welcome!
-current_count=124
+current_count=123
 
 if [ "$count" -gt "$current_count" ]; then
   echo "The PR seems to be introducing new usage of @root_validator and/or @field_validator."