Update templates for external SDK

[davidmrdavid]

The external SDK needs to be imported manually by the user in their profile.ps1. We will need to update our templates to demonstrate how to do this.

We will need to modify the templates for VSCode, and core-tools. There may be more template sources in other places as well that will need updating.

[davidmrdavid]

Superceded by: Azure/azure-functions-powershell-worker#906