[Integration]: Langchain-Permit (#29867)
## Which area of LangChain is being modified?
- This PR adds a new "Permit" integration to the `docs/integrations/`
folder.
- Introduces two new Tools (`LangchainJWTValidationTool` and
`LangchainPermissionsCheckTool`)
- Introduces two new Retrievers (`PermitSelfQueryRetriever` and
`PermitEnsembleRetriever`)
- Adds demo scripts in `examples/` showcasing usage.
## Description of Changes
- Created `langchain_permit/tools.py` for JWT validation and permission
checks with Permit.
- Created `langchain_permit/retrievers.py` for custom Permit-based
retrievers.
- Added documentation in `docs/integrations/providers/permit.ipynb` (or
`.mdx`) to explain setup, usage, and examples.
- Provided sample scripts in `examples/demo_scripts/` to illustrate
usage of these tools and retrievers.
- Ensured all code is linted and tested locally.
Thank you again for reviewing!
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Co-authored-by: Chester Curme <chester.curme@gmail.com>
