Wizard: disable adding empty user tabs

When creating an empty user, the "+" sign gets hidden, and only pops back up if at least user name, psswd, or ssh key is filed out.

Fixes #3114

src/Components/CreateImageWizard/steps/Users/components/UserInfo.tsx

@@ -149,6 +149,7 @@ const UserInfo = () => {
         activeKey={activeTabKey}
         onSelect={onSelect}
         onAdd={onAdd}
+        isAddButtonDisabled={stepValidation.disabledNext}
         onClose={onClose}
         ref={tabComponentRef}
       >