Add sample to illustrate the use of CLU

[ceciliaavila]

Description

As LUIS will soon be retired, it could be useful to have a sample that illustrates how to configure a bot to use the new Custom Language Understanding (CLU) resource.

Describe the solution you'd like

A bot sample configured with CLU.

Describe alternatives you've considered

Create a new sample or update the existing CoreBot that is using LUIS.