Issues with running the quickstart demo

This is the acs-ca-demo linked at https://techcommunity.microsoft.com/t5/azure-communication-services/build-2023-transforming-customer-experiences-with-automated-ai/ba-p/3827857

Branch -[callautomation-openai-sample-csharp](https://github.com/Azure-Samples/communication-services-dotnet-quickstarts/tree/callautomation-openai-sample-csharp/callautomation-openai-sample-csharp)

### This issue is for a: (mark with an `x`)
```
- [x] bug report -> please search issues before submitting
- [ ] feature request
- [x ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```
1. DevTunnels has an issue registering for event grid. Tried with ngrok and it seems to register.
2. Unable to get answer from Azure Cognitive Services for

```
var options = new AnswerCallOptions(incomingCallContext, callbackUri)
{
AzureCognitiveServicesEndpointUrl = new Uri(cognitiveServicesEndpoint)
};

AnswerCallResult answerCallResult = await client.AnswerCallAsync(options);
Console.WriteLine($"Answer call result: {answerCallResult.CallConnection.CallConnectionId}");
```
with error message

```
fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
An unhandled exception has occurred while executing the request.
Azure.RequestFailedException: Service Principal for the Azure Communication Service Resource is not configured.
Status: 400 (Bad Request)
ErrorCode: 8567

Content:
{"error":{"code":"8567","message":"Service Principal for the Azure Communication Service Resource is not configured."}}
```
Where do we add the Cognitive services multi-service account key for this access from the code?
### Minimal steps to reproduce
> Follow the readme guide

### Any log messages given by the failure
>```
fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
An unhandled exception has occurred while executing the request.
Azure.RequestFailedException: Service Principal for the Azure Communication Service Resource is not configured.
Status: 400 (Bad Request)
ErrorCode: 8567

Content:
{"error":{"code":"8567","message":"Service Principal for the Azure Communication Service Resource is not configured."}}
```

### Expected/desired behavior
> No trouble connecting devtunnels
and ability for cog svs to respond back for the incoming call?

Start with the README for the callautomation-openai-sample-csharp branch and trace the AnswerCallAsync entry point shown in the issue. Reproduce the DevTunnels Event Grid registration problem and the 8567 service-principal error, then verify the documented configuration supports both incoming-call responses and Cognitive Services access.

Written by the indexing model from the issue text.