add comment to change of class accessibility

Author: Benjosh95

templates/java/api.mustache

@@ -56,6 +56,7 @@ import cloud.stackit.sdk.core.config.CoreConfiguration;
 import cloud.stackit.sdk.core.exception.ApiException;
 
 {{#operations}}
+// Package-private access to enforce service-specific API usage (DefaultApi => <ServiceName>Api) 
 class {{classname}} {
     private ApiClient localVarApiClient;
     private int localHostIndex;