Support for Digital Ocean registry

[bbrefeld]

Recently I started using VSCode and noticed I was unable to connect to the Digital Ocean registry through the extension.

After some communication with support I got the following message from Digital Ocean:

"After digging further into this, the issue is that Visual Studio is trying to authenticate using the endpoint v2/registry/auth whereas we use /v2/registry/docker-credentials for authentication hence the 404 error"

Would it be possible to add support for this registry?

[bwateratmsft]

We've been tracking registries in #869. I added Digital Ocean to the list.