Add note about upgrading OpenTofu versions

.gitlab-ci.yml

@@ -26,9 +26,8 @@ stages:
 
 variables:
   # Pipeline configuration
-  
   DOCKER_DIND_IMAGE: "docker:24.0.7-dind"
-  #
+
   # OpenTofu variables
   LATEST_OPENTOFU_VERSION: '1.6.0'
 

CONTRIBUTING.md

 # Contributing
 
 Please read about CI/CD components and best practices at: https://docs.gitlab.com/ee/ci/components
+
+## Upgrade OpenTofu versions
+
+When adding new OpenTofu versions the following places need to be updated:
+
+| File                                                         | What                                                                                      |
+| ------------------------------------------------------------ | ----------------------------------------------------------------------------------------- |
+| [`templates/full-pipeline.yml`](templates/full-pipeline.yml) | The `default` value and `options` list of the `sepc.inputs.opentofu_versions` entry.      |
+| [`.gitlab-ci.yml`](.gitlab-ci.yml)                           | The `.opentofu_versions.parallel.matrix` list and the `LATEST_OPENTOFU_VERSION` variable. |
+
+All of the above definitions have to match each other.
+We currently need to change it in multiple places, because there is not a good way to share information
+from the templates and the components pipeline defintion - at least in the features we'd like to use them.