feat: Add release banner for NGINX Gateway Fabric 2.0 (#630)

This commit  adds a release banner for NGINX Gateway Fabric 2.0, 
using the new banner mechanism added to the documentation theme. 
It cascades from the index page, appearing at the top of all pages.

Author: ADubhlaoich

_banners/ngf-2.0-release.md

@@ -0,0 +1,7 @@
+{{< banner "notice" "NGINX Gateway Fabric 2.0 is now available" >}}
+
+NGINX Gateway Fabric 2.0 has released! Follow [this guide]({{< ref "/ngf/upgrading-ngf.md" >}}) to upgrade from 1.x to 2.0.
+
+For 1.x, checkout [an older version](https://github.com/nginx/documentation/commit/0be97114d93be0f44acff8711f31bf0b6448dd94) of documentation.
+
+{{< /banner >}}

content/ngf/_index.md

@@ -1,4 +1,10 @@
 ---
 title: "NGINX Gateway Fabric"
 url: /nginx-gateway-fabric/
+cascade:
+    banner:
+        enabled: true
+        type: deprecation
+        start-date: 2025-05-30
+        md: /_banners/ngf-2.0-release.md
 ---

go.sum

@@ -1,8 +1,2 @@
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