Add Container Mapping support to MSDO

This PR integrates support for Container Mapping with the existing MSDO task.

This PR adds new modes - PreTask and PostTask that signify the pre-and-post job of the decorators
PreTask mode sets the start time variable
PostTask mode fetches the Docker images that were build on this run and encodes the output for the backend to follow
Adds tests for the Container Mapping workflows
Adds new interfaces, classes to make the code more future friendly and durable
Defines new commands in build.proj to make development easier

microsoft / security-devops-azdevops