Add get badge icon method

src/Interface/BadgeableInterface.php

@@ -17,5 +17,12 @@ interface BadgeableInterface
      * @return BadgeColour Colour of badge to render
      */
     public function getBadgeColour(): BadgeColour;
+
+    /**
+     * Get the badge icon name
+     *
+     * @return ?string Icon name
+     */
+    public function getBadgeIcon(): string;
 }