port: CQA to support TokenCredential instead of key

[sw-joelmut]

Related DotNet issue microsoft/botbuilder-dotnet#6889
#minor

Description

This PR adds the ability to use a Managed Identity ClientId to authenticate to the Language service.

Specific Changes

• Added managedIdentityClientId property to the QnAMakerDialog config.
• Added withEndpointKey and withManagedIdentityClientId methods to the QnAMakerDialog class to configure which authentication the request will use.
• Added the ability to detect and get the MSI token in the httpRequestUtils file.

Testing

The following image shows the bot working with both authorization types.