nixos/netbird: update docs & release notes

nixos/doc/manual/redirects.json

···
   "module-services-netbird-multiple-connections": [
     "index.html#module-services-netbird-multiple-connections"
   ],
+  "module-services-netbird-firewall": [
+    "index.html#module-services-netbird-firewall"
+  ],
+  "module-services-netbird-customization": [
+    "index.html#module-services-netbird-customization"
+  ],
   "module-services-mosquitto": [
     "index.html#module-services-mosquitto"
   ],

nixos/doc/manual/release-notes/rl-2505.section.md

···
   as before, you can use plugins like `python3Packages.jax-cuda12-plugin`.
 
 
+- `services.netbird.tunnels` was renamed to [`services.netbird.clients`](#opt-services.netbird.clients),
+  hardened (using dedicated less-privileged users) and significantly extended.
+
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
 ## Other Notable Changes {#sec-release-25.05-notable-changes}

nixos/modules/services/networking/netbird.md

···
 
 ```nix
 {
-  services.netbird.clients.default = {
+  services.netbird.clients.wt0 = {
     port = 51820;
-    interface = "wt0";
     name = "netbird";
+    interface = "wt0";
     hardened = false;
   };
 }