css: add external-link utility class

Adds an .external-link utility class, to be used together with the
existing .link utility, for adding the correct styles to the open_in_new
icon without having to duplicate the markup each time.

Signed-off-by: David Karlsson <35727626+dvdksn@users.noreply.github.com>

assets/css/global.css

@@ -18,6 +18,12 @@
     @apply text-blue-light underline underline-offset-2 dark:text-blue-dark;
   }
 
+  .external-link {
+    .icon:after {
+      @apply text-base ml-1;
+    }
+  }
+
   .invertible {
     @apply dark:hue-rotate-180 dark:invert dark:filter;
   }