docs: add notebook for langchain-salesforce package (#29800)

**Description:**  
This PR adds a Jupyter notebook that explains the features,
installation, and usage of the
[`langchain-salesforce`](https://github.com/colesmcintosh/langchain-salesforce)
package. The notebook includes:
- Setup instructions for configuring Salesforce credentials  
- Example code demonstrating common operations such as querying,
describing objects, creating, updating, and deleting records

**Issue:**  
N/A

**Dependencies:**  
No new dependencies are required.

**Tests and Docs:**  
- Added an example notebook demonstrating the usage of the
`langchain-salesforce` package, located in `docs/docs/integrations`.

**Lint and Test:**  
- Ran `make format`, `make lint`, and `make test` successfully.

---------

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

libs/packages.yml

@@ -429,6 +429,11 @@ packages:
   repo: langchain-ai/langchain
   downloads: 9521
   downloads_updated_at: '2025-02-13T23:35:48.490391+00:00'
+- name: langchain-salesforce
+  path: .
+  repo: colesmcintosh/langchain-salesforce
+  downloads: 0
+  downloads_updated_at: '2025-02-13T23:35:48.490391+00:00'
 - name: langchain-discord-shikenso
   path: .
   repo: Shikenso-Analytics/langchain-discord