Privatize CoA deployments by default

[jsaun]

1. Make private networking the default option when deploying a new CoA instance.
2. Automate all work currently needed to be done manually to create a private CoA instance from the wiki https://github.com/microsoft/CromwellOnAzure/wiki/Setting-up-private-networking-for-Cromwell-on-Azure

Subtasks:
Remove the --private-networking flag and add an --public-networking flag to revert to previous behavior.
Create CoA Vnet with NSG and inbound connections blocked.
microsoft/ga4gh-tes#209 Cache Docker images in Azure Storage as block blobs
Create private ACR for TES, Cromwell & TriggerService images, and call ACR to import those images into the repo. (Potentially not needed if its possible to start AKS from a container stored in blob storage)