add: openwrt import webui assets 2.3.0

import webui assets from latest 2.3.0 release packages for OpenWrt releases as well.

wrt/files/webui/_headers

@@ -0,0 +1,12 @@
+# for netlify hosting
+# https://docs.netlify.com/routing/headers/#syntax-for-the-headers-file
+
+/*
+  X-Frame-Options: DENY
+  X-XSS-Protection: 1; mode=block
+  X-Content-Type-Options: nosniff
+  Referrer-Policy: same-origin
+/*.css
+  Cache-Control: public, max-age=31536000, immutable
+/*.js
+  Cache-Control: public, max-age=31536000, immutable