Set User Agent to grpc workflow client in workhorse

What does this MR do and why?

This MR adds User Agent header to DAP client in workhorse. This allows us to figure out the errors by the application client in DWS dashboard.

Related to https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/ai-assist/-/issues/1393+ and Add metadata to metrics and events (gitlab-org/modelops/applied-ml/code-suggestions/ai-assist#1571).

References

DWS log (Web UI)::

{
    "event": "Finished ExecuteWorkflow RPC",
    "logger": "grpc",
    "level": "info",
    "correlation_id": "01K82J2T0SY5GDH9K7ES8679WE",
    "gitlab_global_user_id": "MMwwCtYAHYpnJyB07tz+J1HZ5cYKDB28u0ir4JRm+Gc=",
    "workflow_id": "407",
    "duration_s": 5.274897960996896,
    "request_arrived_at": "2025-10-21T04:57:47.870250+00:00",
    "cpu_s": 0.303933357,
    "grpc_type": "BIDI_STREAM",
    "grpc_service_name": "DuoWorkflow",
    "grpc_method_name": "ExecuteWorkflow",
    "servicer_context_code": "OK",
    "servicer_context_details": "workflow execution success: require_input",
    "gitlab_host_name": "gdk.test",
    "gitlab_realm": "saas",
    "gitlab_instance_id": "f6f95e20-e282-411f-9fb8-81ddf33b35a2",
    "gitlab_authentication_type": "oidc",
    "gitlab_version": "18.6.0",
    "user_agent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/141.0.0.0 Safari/537.36 gitlab-workhorse/11-10-0cfa69752d8-74ffd66ae-ee-362094-g61f18c6c90a2 grpc-go/1.73.0",
    "workflow_definition": "chat",
    "timestamp": "2025-10-21T04:57:53.145252Z"
}

DWS log (editor extension - websocket):

{
    "event": "Finished ExecuteWorkflow RPC",
    "logger": "grpc",
    "level": "info",
    "correlation_id": "01K82HSYVFTZQZ8QG53Q0KX613",
    "gitlab_global_user_id": "MMwwCtYAHYpnJyB07tz+J1HZ5cYKDB28u0ir4JRm+Gc=",
    "workflow_id": "426",
    "duration_s": 4.794210850002855,
    "request_arrived_at": "2025-10-21T04:52:57.786354+00:00",
    "cpu_s": 0.41881001399999906,
    "grpc_type": "BIDI_STREAM",
    "grpc_service_name": "DuoWorkflow",
    "grpc_method_name": "ExecuteWorkflow",
    "servicer_context_code": "OK",
    "servicer_context_details": "workflow execution success: require_input",
    "gitlab_host_name": "gdk.test",
    "gitlab_realm": "saas",
    "gitlab_instance_id": "f6f95e20-e282-411f-9fb8-81ddf33b35a2",
    "gitlab_authentication_type": "oidc",
    "gitlab_version": "18.6.0",
    "user_agent": "visual-studio-code/1.105.1 gitlab-workflow/6.49.11 gitlab-language-server/8.24.0 gitlab-workhorse/11-10-0cfa69752d8-74ffd66ae-ee-362094-g61f18c6c90a2 grpc-go/1.73.0",
    "workflow_definition": "chat",
    "timestamp": "2025-10-21T04:53:02.580623Z"
}

Screenshots or screen recordings

Before	After

How to set up and validate locally

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