Add openstack (#10132)

* Adding Openstack - Update free-courses-en.md

Added in Openstack into the cloud section with the OpenStack tutorial by FreeCodeCamp and the OpenStack CERN admin guide.

* Update free-courses-en.md

Changes to positioning and alphabetical order.

* Update free-courses-en.md

* Update free-programming-books-subjects.md

* Update free-programming-books-subjects.md

books/free-programming-books-subjects.md

@@ -179,6 +179,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Learn Azure in a Month of Lunches](https://clouddamcdnprodep.azureedge.net/gdc/2014519/original) - Iain Foulds (PDF)
 * [Monitoring Modern Infrastructure](https://www.datadoghq.com/ebook/monitoring-modern-infrastructure/) *(account required)*
 * [Multi-tenant Applications for the Cloud, 3rd Edition](https://www.microsoft.com/en-us/download/details.aspx?id=29263)
+* [Openstack CERN Admin guide](https://clouddocs.web.cern.ch/index.html)
 * [OpenStack Operations Guide](https://docs.openstack.org/ops-guide/index.html)
 * [Streamline microservice management with Istio Service Mesh](https://developers.redhat.com/books/introducing-istio-service-mesh-microservices/) *(account required)*
 * [The Developer’s Guide to Azure](https://azure.microsoft.com/en-us/campaigns/developer-guide/)