Document advanced use cases for GitLab CI/CD and private container image registries

[0x2b3bfa0]

• [ ] AWS instance profiles as per https://github.com/iterative/terraform-provider-iterative/issues/602#issuecomment-1145964625

• [ ] Configuration as part of the workflow variables, as in e.g.

  variables:
  AWS_ACCOUNT: 000000000000
  AWS_DEFAULT_REGION: us-east-1
  AWS_REGISTRY: ${AWS_ACCOUNT}.dkr.ecr.${AWS_DEFAULT_REGION}.amazonaws.com
  AWS_CONTAINER_IMAGE: ${AWS_REGISTRY}/example:latest
  DOCKER_AUTH_CONFIG: '{"credHelpers": {"${AWS_REGISTRY}": "ecr-login"}}'
  
  build:
  rules:
    - changes: [Dockerfile, .gitlab-ci.yml]
  services:
    - docker:dind
  image: docker
  script:
    - docker run --env AWS_ACCESS_KEY_ID --env AWS_SECRET_ACCESS_KEY --env AWS_SESSION_TOKEN --env AWS_DEFAULT_REGION amazon/aws-cli ecr get-login-password |
      docker login --username AWS --password-stdin ${AWS_REGISTRY}
    - docker build --tag ${AWS_CONTAINER_IMAGE} . 
    - docker push ${AWS_CONTAINER_IMAGE}
  
  launch:
  image: iterativeai/cml:0-dvc2-base1
  script: >
    cml runner launch
    --cloud=aws
    --cloud-region=$AWS_DEFAULT_REGION
    --cloud-type=m5.2xlarge    
    --cloud-hdd-size=32
    --labels=cml
  
  train:
  needs: [launch]
  tags: [cml]
  image: ${AWS_CONTAINER_IMAGE}
  script:
    - echo hello world