GitLab CI/CD: Staged Deployment (dev -> stage -> prod)

.gitlab-ci.yml

# When deploy-dev auto-deploys

# When deploy-dev succeeds, the (⏵) button for the deploy-stage stage shows up
# When deploy-dev fails,    the (⏵) button for the deploy-stage stage does NOT show up

# Same for the deploy-prod stage

stages:
  - deploy-dev
  - deploy-test
  - deploy-stage

deploy-dev:
  stage: deploy-dev
  environment: Development
  script:
    - env

deploy-stage:
  stage: deploy-stage
  environment: Staging
  script:
    - env
  when: manual
  needs:
    - deploy-dev

deploy-prod:
  stage: deploy-prod
  environment: Production
  script:
    - env
  when: manual
  needs:
    - deploy-stage