add container registry and build task to default template

[joshgav]

As part of the default Azure template, create a container registry and a container build task and/or build step to build and maintain the container described by the repo's main Dockerfile.

Also add a registry webhook and trigger refresh of the App Service web app whenever the container is rebuilt.

With this in place, a user will be able to update code in the app and git push it to have the container rebuilt and refreshed.