Add an Azure AI Search context provider

[shibayan]

Priority

P3

Goal

Provide a reusable Azure AI Search retrieval provider using the existing ContextProvider extension point.

Scope

• Configure index, query, credential, filtering, and result limits.
• Retrieve and format grounded context before agent execution.
• Propagate user and tenant filters from the hosted execution context.
• Add mockable tests, documentation, and a RAG sample.

Acceptance criteria

• The provider can retrieve relevant documents and attach source metadata.
• Tenant and authorization filters cannot be bypassed by model-generated input.
• Query and result size limits are configurable.
• Transport behavior is mockable without live Azure resources.
• A hosted RAG sample documents required Azure configuration.

Dependency

Blocked by the common hosted execution context for multi-tenant filtering.