The momento-datetime header is missing from the response even when the accept-datetime request header is sent

When testing the time-based access feature in the C++ AppConfig client SDK (for an endpoint like `GetLabels`), I don't see the `Memento-DateTime` header being returned in the response back from the service as described in the doc example here:
https://learn.microsoft.com/en-us/azure/azure-app-configuration/rest-api-labels?pivots=v23-10#time-based-access

I see a `"date"` header, which is the time when request was received, but not the `Memento-DateTime` header corresponding to the value in the Accept-DateTime header in the request (which was "Fri, 10 Jan 2025 00:00:00 GMT" ).

This requires further investigation to root cause the issue.

Here's the response headers I see:

```C++
GetLabelsOptions options;
options.Name = "paging-*";
options.AcceptDatetime = "Fri, 10 Jan 2025 00:00:00 GMT";

GetLabelsPagedResponse labelsPage = configurationClient.GetLabels("accept", options);
```

The service team is able to see the expected response header testing the endpoint directly using REST API client: