.Net: Add Usage Metadata for ChatClientChatCompletionService Adapter

[RogerBarreto]

Motivation and Context

As part of Agents code-base is commong practice now to acquire Usage from the ChatMessageContent.Metadata, although is different how this is done with the new Microsoft.Extensions.AI relying on the UsageDetails or UsageContent to avoid any disruption when migrating Agents to use the IChatClient. This change was made, so old code can still function.

[markwallace-microsoft]

Unrelated integration test failure

[xUnit.net 00:00:40.22]     SemanticKernel.IntegrationTests.Connectors.OpenAI.OpenAIChatCompletionNonStreamingTests.ChatCompletionWithWebSearchAsync [FAIL]
[xUnit.net 00:00:40.22]       Assert.NotEmpty() Failure: Collection was empty
[xUnit.net 00:00:40.22]       Stack Trace:
[xUnit.net 00:00:40.22]         /home/runner/work/semantic-kernel/semantic-kernel/dotnet/src/IntegrationTests/Connectors/OpenAI/OpenAIChatCompletion_NonStreamingTests.cs(162,0): at SemanticKernel.IntegrationTests.Connectors.OpenAI.OpenAIChatCompletionNonStreamingTests.ChatCompletionWithWebSearchAsync()
[xUnit.net 00:00:40.22]         --- End of stack trace from previous location ---

[markwallace-microsoft]

Unrelated integration test failure. We are seeing multiple failures related to this endpoint.

[xUnit.net 00:01:54.64]     SemanticKernel.IntegrationTests.Connectors.OpenAI.OpenAIChatCompletionNonStreamingTests.ChatCompletionWithAudioInputAndOutputAsync [FAIL]
[xUnit.net 00:01:54.64]       Microsoft.SemanticKernel.HttpOperationException : Service request failed.
[xUnit.net 00:01:54.64]       Status: 503 (Service Unavailable)
[xUnit.net 00:01:54.64]       
[xUnit.net 00:01:54.64]       ---- System.ClientModel.ClientResultException : Service request failed.
[xUnit.net 00:01:54.64]       Status: 503 (Service Unavailable)