Draft: Duo Workflow: Self-hosted models poc

What does this MR do and why?

This MR sends self-hosted metadata when an agent flow is initialized via Workhorse/Websockets. The metadata then intercepted by the server and the correct self-hosted model is called: feat: self-hosted model metadata (gitlab-org/modelops/applied-ml/code-suggestions/ai-assist!2912 - merged)

Testing

1. Make sure that Duo Agentic Chat is available locally:

• Classic Duo Chat is available: current_user.can?(:access_duo_chat, project) is true
• duo_agentic_chat feature flag is enabled
• Duo Workflow Service is available:
  • duo_workflow feature is enabled
  • configured config/gitlab.yml

  development:
    duo_workflow:
      service_url: 0.0.0.0:50052
      secure: false

2. Feature flag duo_workflow_workhorse is enabled and Duo Agentic Chat icon is shown near classic Duo Chat button
3. Visit http://gdk.test:3333 to match the Workhorse port to be able to connect to it via Websockets
4. Perform a request like hello in the Agentic Chat
5. Verify that the Anthropic Bedrock model is called