Rename Nested Steps

[RyanTimoney]

Currently, the term steps is being used at the Servicer level, and separately for things like the service adapters. This results in a service looking like this:

  docker_example:
    provider: gcloud
    service_type: docker_image
    steps:
      build:
        config:
          # The service adapter handles things nested at this level and deeper
          steps:
            - type: build
              args:
                image: demo-image
                dockerfile: Dockerfile

There's no way to recognize here that the steps nested within the service adapter have no relationship with the steps run at the top level of Servicer. It would improve readability to deprecate the service adapter steps with steps-sa, or similar, to clearly distinguish them from the steps run at the top level.