Fix using deprecated global declarations in example .gitlab-ci.ymls

* See: https://docs.gitlab.com/ee/ci/yaml/#globally-defined-image-services-cache-before_script-after_script

doc/user/infrastructure/index.md

@@ -376,17 +376,18 @@ can configure this manually as follows:
 ### Example `.gitlab-ci.yaml` file
 
 ```yaml
-image: registry.gitlab.com/gitlab-org/terraform-images/stable:latest
-
-variables:
-  TF_ROOT: ${CI_PROJECT_DIR}/environments/example/production
-  TF_ADDRESS: ${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/terraform/state/example-production
+default:
+  image: registry.gitlab.com/gitlab-org/terraform-images/stable:latest
 
-cache:
+  cache:
     key: example-production
     paths:
       - ${TF_ROOT}/.terraform
 
+variables:
+  TF_ROOT: ${CI_PROJECT_DIR}/environments/example/production
+  TF_ADDRESS: ${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/terraform/state/example-production
+
 before_script:
   - cd ${TF_ROOT}
 
@@ -436,13 +437,14 @@ apply:
 Starting with 13.2, you can display multiple reports on the Merge Request page. The reports will also display the `artifacts: name:`. See example below for a suggested setup.
 
 ```yaml
-image:
+default:
+  image:
     name: registry.gitlab.com/gitlab-org/gitlab-build-images:terraform
     entrypoint:
       - '/usr/bin/env'
       - 'PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'
 
-cache:
+  cache:
     paths:
       - .terraform