CI Server Workloads for ContainerBuilds

[baronfel]

We should cover common CI/CD system workflows in an aim to make it easier, faster, and more secure to build containers in CI/CD systems.

Today, we cover the following workflows:

• build single-architecture containers

We need to cover the following scenarios to address key user scenarios for container building:

• [x] #87
• [x] https://github.com/dotnet/sdk-container-builds/issues/609
• [ ] #583 to remove the need to spawn registry:2 containers to store intermediate images