feat(notification-toast): add css var for z-index (#1041)

* feat: adding autoHide to toast

* feat: adding autoHide to toast storybook page

* refactor: change static z-index to css variable

packages/components/src/components/notification-toast/notification-toast.css

@@ -15,6 +15,7 @@
   --width-icon-container: 48px;
   --radius: var(--telekom-radius-standard);
   --background: var(--telekom-color-background-surface);
+  --z-index: 1;
   /* FIXME:TOKEN not sure what elevation to use here */
   --box-shadow: var(--telekom-shadow-raised-standard);
 
@@ -49,7 +50,7 @@
 .notification-toast {
   width: var(--width);
   opacity: 0;
-  z-index: 1;
+  z-index: var(--z-index);
   position: fixed;
   background: var(--background);
   box-shadow: var(--box-shadow);