chore: import upstream snapshot with attribution

dotnet/samples/GettingStartedWithAgents/A2A/Step01_A2AAgent.cs

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+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Text.Json;
+using A2A;
+using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.Agents;
+using Microsoft.SemanticKernel.Agents.A2A;
+
+namespace GettingStarted.A2A;
+
+/// <summary>
+/// This example demonstrates similarity between using <see cref="A2AAgent"/>
+/// and other agent types.
+/// </summary>
+public class Step01_A2AAgent(ITestOutputHelper output) : BaseAgentsTest(output)
+{
+    [Fact]
+    public async Task UseA2AAgent()
+    {
+        // Create an A2A agent instance
+        var url = TestConfiguration.A2A.AgentUrl;
+        using var httpClient = CreateHttpClient();
+        var client = new A2AClient(url, httpClient);
+        var cardResolver = new A2ACardResolver(url, httpClient);
+        var agentCard = await cardResolver.GetAgentCardAsync();
+        Console.WriteLine(JsonSerializer.Serialize(agentCard, s_jsonSerializerOptions));
+        var agent = new A2AAgent(client, agentCard);
+
+        // Invoke the A2A agent
+        await foreach (AgentResponseItem<ChatMessageContent> response in agent.InvokeAsync("List the latest invoices for Contoso?"))
+        {
+            this.WriteAgentChatMessage(response);
+        }
+    }
+
+    [Fact]
+    public async Task UseA2AAgentStreaming()
+    {
+        // Create an A2A agent instance
+        var url = TestConfiguration.A2A.AgentUrl;
+        using var httpClient = CreateHttpClient();
+        var client = new A2AClient(url, httpClient);
+        var cardResolver = new A2ACardResolver(url, httpClient);
+        var agentCard = await cardResolver.GetAgentCardAsync();
+        Console.WriteLine(JsonSerializer.Serialize(agentCard, s_jsonSerializerOptions));
+        var agent = new A2AAgent(client, agentCard);
+
+        // Invoke the A2A agent
+        var responseItems = agent.InvokeStreamingAsync("List the latest invoices for Contoso?");
+        await WriteAgentStreamMessageAsync(responseItems);
+    }
+
+    #region private
+    private bool EnableLogging { get; set; } = false;
+
+    private HttpClient CreateHttpClient()
+    {
+        if (this.EnableLogging)
+        {
+            var handler = new LoggingHandler(new HttpClientHandler(), this.Output);
+            return new HttpClient(handler);
+        }
+
+        return new HttpClient();
+    }
+
+    private static readonly JsonSerializerOptions s_jsonSerializerOptions = new() { WriteIndented = true };
+    #endregion
+}