fix: Update shoot rolling upgrade How-To in light of k8s 1.27

We explicitly reference Kubernetes 1.27. Due to certain UI changes,
we re-create all screenshots and modify the prose accordingly.

docs/howto/kubernetes/gardener/rolling-upgrades.md

@@ -3,75 +3,60 @@ description: How to manually upgrade machine images or Kubernetes versions for G
 ---
 # Conducting rolling upgrades
 
-By default, Kubernetes clusters created with {{k8s_management_service}}
-in {{brand}} are upgraded automatically. Those upgrades take place
-during a specified maintenance window, and you may find out more about
-[what they involve and how they
-work](../../../background/kubernetes/gardener/autoupgrades.md). Besides
-the automatic upgrades, you can manually apply any upgrades available
-for your cluster.
-
-In the following two examples, we first show how to manually upgrade the
-machine image the cluster nodes are based on and then how to upgrade the
-Kubernetes version the cluster uses.
+By default, Kubernetes clusters created with {{k8s_management_service}} in {{brand}} are upgraded automatically.
+Those upgrades take place during a specified maintenance window, and you may find out more about [what they involve and how they work](../../../background/kubernetes/gardener/autoupgrades.md).
+Besides the automatic upgrades, you may manually apply any upgrades available for your cluster.
+
+In the following two examples, we first show how to manually upgrade the machine image the cluster nodes are based on.
+Then, we show how to upgrade the Kubernetes version the cluster uses.
 
 ## Upgrading machine images
 
-In the left-hand vertical pane of the {{gui}}, select Containers →
-[{{k8s_management_service}}](https://{{gui_domain}}/containers/gardener).
-In the central pane, you will see all your {{k8s_management_service}}
-clusters, each on its own row. If a Kubernetes upgrade is available, in
-the *Version* column you will notice a blue :fontawesome-solid-circle-arrow-up: icon, together with
-the new Kubernetes version. Additionally, if there is a new machine
-image version for the cluster nodes, then in the *Worker Groups* column you
-will also notice a blue :fontawesome-solid-circle-arrow-up: icon but no version number.
+In the left-hand vertical pane of the {{gui}}, select Containers → [{{k8s_management_service}}](https://{{gui_domain}}/containers/gardener).
+In the central pane, you will see all your {{k8s_management_service}} clusters, each on its own row.
+If a Kubernetes upgrade is available for a shoot cluster, in the *Version* column you will notice a blue :fontawesome-solid-circle-arrow-up: icon, together with the new Kubernetes version.
+Additionally, if there is a new machine image version for the cluster nodes, then in the *Worker Groups* column you will also notice a blue :fontawesome-solid-circle-arrow-up: icon but no version number.
 
 ![Garden Linux and Kubernetes upgrades available](assets/rollupgr-01.png)
 
-To get more information about the new machine image available, click on
-the cluster row to bring its details up into view, then select the *Worker
-Groups* tab. There, you will see the version of the new machine image.
-To start the upgrade process, click any of the two
-:fontawesome-solid-arrow-up: icons.
+To get more information about the new machine image available, click on the cluster row to bring its details up into view, then select the *Worker Groups* tab.
+There, you will see the version of the new machine image.
+To start the upgrade process, click any of the two :fontawesome-solid-arrow-up: icons.
 
 ![About to start Garden Linux upgrade](assets/rollupgr-02.png)
 
-The upgrade process will start immediately and will take some time to
-complete. A little before and after it is done, there will be no icon in the
-*Worker Groups* column, and the new image version will be displayed in the
-*Image* row of the *Worker Groups* tab. Our example still has an icon in the
-*Version* column. That is because we have not upgraded Kubernetes yet.
+The upgrade process starts immediately and takes some time to complete.
+A little before and after it is done, there is no icon in the *Worker Groups* column, and the new image version is displayed in the
+*Image* row of the *Worker Groups* tab.
+Since we have not upgraded Kubernetes yet, our example still has an icon in the *Version* column.
 
 ![Garden Linux upgraded](assets/rollupgr-03.png)
 
 ## Upgrading Kubernetes
 
-To get the Kubernetes upgrade process going, click the orange
-:material-dots-horizontal-circle: icon on the right of the cluster row.
-In the pop-up menu that appears, you will notice an option named
-*Kubernetes Patch Available*. That one is not always there, but now it
-is and acts as another indicator of an available Kubernetes upgrade.
+To get the Kubernetes upgrade process going, click the orange :material-dots-horizontal-circle: icon on the right of the cluster row.
+In the following example, we go from Kubernetes 1.26 to Kubernetes 1.27; that is the latest version supported at the time of this writing.
+In the pop-up menu that appears, there is an option named *Kubernetes Patch Available*.
+That one is not always there, and when it is acts as yet another indicator of an available Kubernetes upgrade.
 Please select the option by clicking on it.
 
 ![Kubernetes patch available](assets/rollupgr-04.png)
 
-A new pop-up window named *Upgrade Kubernetes Version for:
-<cluster_name>* appears. From the *Version* drop-down menu, you
-may select the new Kubernetes version you want your cluster to upgrade
-to.  When ready, click the blue *Upgrade* button to start the process.
+A new pop-up window named *Upgrade Kubernetes Version for: <cluster_name>* appears.
+From the *Version* drop-down menu, you may select the new Kubernetes version you want your cluster to upgrade to.
+When ready, click the blue *Upgrade* button to start the process.
 
 ![About to start a Kubernetes upgrade](assets/rollupgr-05.png)
 
-You will realize that the upgrade doesn't start right away. Instead, you
-are informed that the cluster is indeed ready for it, but there are some
-notes you might want to read up on before the whole process begins. If
-you do, copy and paste the provided URL into a separate browser tab or
-window. In any case, to actually get the upgrade going, click the
-*Upgrade* button which is now green.
+You will realize that the upgrade doesn't start right away.
+Instead, you are informed that the cluster is indeed ready for it, but there are some notes you might want to read up on before the whole process begins.
+The gist of it is that any existing static kubeconfig will stop working after the upgrade to Kubernetes 1.27, and you will not be able to create a new static kubeconfig.
+You will, however, be able to create [a new certificate-based kubeconfig](kubectl.md).
+To get the upgrade going, click the *Upgrade* button which is now green.
 
 ![Upgrade notes are available](assets/rollupgr-06.png)
 
-After some minutes, the upgrade will be over. The new Kubernetes version
-will be visible in the *Version* column of the cluster row.
+After some minutes, the upgrade will be over.
+The new Kubernetes version will be visible in the *Version* column of the cluster row.
 
 ![Kubernetes successfully upgraded](assets/rollupgr-07.png)