Add support for MSI in the CQA sample

[sw-joelmut]

[!IMPORTANT] This PR requires the fix and release of the issue https://github.com/microsoft/botbuilder-dotnet/issues/6889

Description

This PR adds support for User Managed Identity to the CQA sample. Providing a way to choose between using the EndpointKey or the MSI resource to authenticate to the Language service.

Proposed Changes

• Updated RootDialog to support both EndpointKey and MSI auth type for CQA resource.
• Updated README.md to include the new MSI option and the required configuration.
• Updated appsettings.json to include the new LanguageManagedIdentityClientId property.

Testing

The following image shows the both types of authentication working.