community: add Valthera integration (#30105)

```markdown
**Description:**  
This PR integrates Valthera into LangChain, introducing an framework designed to send highly personalized nudges by an LLM agent. This is modeled after Dr. BJ Fogg's Behavior Model. This integration includes:

- Custom data connectors for HubSpot, PostHog, and Snowflake.
- A unified data aggregator that consolidates user data.
- Scoring configurations to compute motivation and ability scores.
- A reasoning engine that determines the appropriate user action.
- A trigger generator to create personalized messages for user engagement.

**Issue:**  
N/A

**Dependencies:**  
N/A

**Twitter handle:**  
- `@vselvarajijay`

**Tests and Docs:**  
- `docs/docs/integrations/tools/valthera` 
- `https://github.com/valthera/langchain-valthera/tree/main/tests`

```

---------

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

libs/packages.yml

@@ -506,3 +506,7 @@ packages:
   repo: ContextualAI//langchain-contextual
   downloads: 432
   downloads_updated_at: '2025-03-09T01:40:49.430540+00:00'
+- name: langchain-valthera
+  name_title: Valthera
+  path: .
+  repo: valthera/langchain-valthera