[Documentation] Update vector_store.url description

[atagunay]

Description

The vector_store.url attribute is required for both Azure AI Search and Cosmos DB. However, the current documentation only mentions Azure AI Search. This update ensures consistent and accurate guidance by including Cosmos DB as well.

Current document: https://microsoft.github.io/graphrag/config/yaml/#fields_3

Checklist

• I have tested these changes locally.
• I have reviewed the code changes.
• I have updated the documentation (if necessary).
• I have added appropriate unit tests (if applicable).

[atagunay]

@microsoft-github-policy-service agree