Updating/work-with this template for Azd Devcontainer feature.

[v-xuto]

We are updating this template to support new features in Github Action and Azd Devcontainer.

For the Azd Devcontainer feature: We will remove dockerfile in .devcontainer folder and add the following code in devcontainer.json file,

"ghcr.io/azure/azure-dev/azd:latest": {}

and image also need to be add instead of build.

@rajeshkamal5050 , @achandmsft, @rcarun for notification.