fix(operator): Scale statefulset to 0 to prepare for update (#30450)

When performing a keycloak update, the operator is supposed to make sure that
potential database migrations are run with only one pod active. This change
makes the operator scale down the stateful set to zero pods in preparation for
the update. The next reconciliation loop will scale the stateful set back up
and change the image, making sure migrations are being run on the first pod
that is brought up. This also makes sure that the rollover works even if the
infinispan versions are incompatible. (ref: #30449)

Signed-off-by: Schmidt, Sascha (sasschmidt) <sascha.schmidt@breuninger.de>
(cherry picked from commit 13ef6fb1c8)

operator/src/main/java/org/keycloak/operator/controllers/KeycloakDeploymentDependentResource.java

@@ -461,13 +461,13 @@ public class KeycloakDeploymentDependentResource extends CRUDKubernetesDependent
         var reconciledContainer = reconciledDeployment.getSpec().getTemplate().getSpec().getContainers().get(0);
 
         if (!previousContainer.getImage().equals(reconciledContainer.getImage())
-                && previousDeployment.getStatus().getReplicas() > 1) {
+                && previousDeployment.getStatus().getReplicas() > 0) {
             // TODO Check if migration is really needed (e.g. based on actual KC version); https://github.com/keycloak/keycloak/issues/10441
             Log.info("Detected changed Keycloak image, assuming Keycloak upgrade. Scaling down the deployment to one instance to perform a safe database migration");
             Log.infof("original image: %s; new image: %s", previousContainer.getImage(), reconciledContainer.getImage());
 
             reconciledContainer.setImage(previousContainer.getImage());
-            reconciledDeployment.getSpec().setReplicas(1);
+            reconciledDeployment.getSpec().setReplicas(0);
 
             reconciledDeployment.getMetadata().getAnnotations().put(Constants.KEYCLOAK_MIGRATING_ANNOTATION, Boolean.TRUE.toString());
         }