.Net: Add a new orchestration sample that uses different agent types

[markwallace-microsoft]

Motivation and Context

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[Copilot]

Pull Request Overview

This PR introduces a new orchestration sample that demonstrates using different agent types and refactors how agents are created and handled in existing tests and channels.

• Refactor in BaseOrchestrationTest: renamed CreateAgent to CreateChatCompletionAgent, added async methods CreateOpenAIAssistantAgentAsync and CreateAzureAIAgentAsync for new agent types.
• Enhanced error handling in both OpenAIAssistantChannel and AzureAIChannel with unified exception messages and empty‐message filtering in message factories.
• Added Step06_DifferentAgentTypes sample covering concurrent, sequential, group chat, and handoff orchestrations with diverse agent implementations.

Reviewed Changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
dotnet/src/InternalUtilities/samples/AgentUtilities/BaseOrchestrationTest.cs	Refactored agent-creation API and added new async factory methods.
dotnet/src/Agents/OpenAI/OpenAIAssistantChannel.cs	Wrapped channel send errors and rethrew with a consistent message.
dotnet/src/Agents/AzureAI/AzureAIChannel.cs	Similar error wrapping plus a catch-all for unexpected exceptions.
dotnet/src/Agents/OpenAI/Internal/AssistantMessageFactory.cs	Added logic to skip empty text messages.
dotnet/src/Agents/AzureAI/Internal/AgentMessageFactory.cs	Added logic to skip empty text messages.
dotnet/samples/GettingStartedWithAgents/Orchestration/Step06_DifferentAgentTypes.cs	New sample showcasing multiple orchestration patterns with varied agent types.
(other samples)	Updated calls from CreateAgent to CreateChatCompletionAgent and corrected typos.

Comments suppressed due to low confidence (1)

dotnet/samples/GettingStartedWithAgents/Orchestration/Step06_DifferentAgentTypes.cs:307

• [nitpick] In OrderRefundPlugin, the method is named ProcessReturn but handles refunds. Consider renaming it to ProcessRefund to clearly reflect its purpose and avoid confusion with the return plugin.

        public string ProcessReturn(string orderId, string reason) => $"Refund for order {orderId} has been processed successfully.";