docs: Add documentation on how to contribute a Vector DB provider and update testing documentation (#3093)

# What does this PR do?

- Adds documentation on how to contribute a Vector DB provider.
- Updates the testing section to be a little friendlier to navigate.
- Also added new shortcut for search so that `/` and `⌘ K` or `ctrl+K`
trigger search


<img width="1903" height="1346" alt="Screenshot 2025-08-11 at 10 10
12 AM"
src="https://github.com/user-attachments/assets/6995b3b8-a2ab-4200-be72-c5b03a784a29"
/>

<img width="1915" height="1438" alt="Screenshot 2025-08-11 at 10 10
25 AM"
src="https://github.com/user-attachments/assets/1f54d30e-5be1-4f27-b1e9-3c3537dcb8e9"
/>

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<!-- Closes #[issue-number] -->

## Test Plan
<!-- Describe the tests you ran to verify your changes with result
summaries. *Provide clear instructions so the plan can be easily
re-executed.* -->

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

docs/source/contributing/index.md

@@ -2,14 +2,28 @@
 ```{include} ../../../CONTRIBUTING.md
 ```
 
-See the [Adding a New API Provider](new_api_provider.md) which describes how to add new API providers to the Stack.
+## Testing
 
+See the [Test Page](testing.md) which describes how to test your changes.
+```{toctree}
+:maxdepth: 1
+:hidden:
+:caption: Testing
 
+testing
+```
 
+## Adding a New Provider
+
+See the [Adding a New API Provider Page](new_api_provider.md) which describes how to add new API providers to the Stack.
+
+See the [Vector Database Page](new_vector_database.md) which describes how to add a new vector databases with Llama Stack.
+
+See the [External Provider Page](../providers/external/index.md) which describes how to add external providers to the Stack.
 ```{toctree}
 :maxdepth: 1
 :hidden:
 
 new_api_provider
-testing
+new_vector_database
 ```