Add Higress to the networking plugins section in the installation guide (#6540)

* Add Higress as a recommended networking plugin

Add Higress to the networking plugins section in the installation guide.
Higress is a next-generation cloud-native gateway that provides enhanced
traffic governance, security protection, and observability for Knative
services with WASM plugin extensibility.

Change-Id: I6cb9efcf39dd0377314400213b11b685915b002c
Co-developed-by: Cursor <[email protected]>
Reference: https://www.alibabacloud.com/blog/higress-a-best-practice-for-knative-ingress-gateway_600549

* Clarify Higress as third-party integration

Add clear designation that Higress integration is third-party
and not managed by the Knative community, as requested by reviewers.

Change-Id: I98d3454da8a8e4cef74ac5a88d8b0f3017426c15
Co-developed-by: Cursor <[email protected]>

* Simplify Higress description and add official website link

- Add link to Higress official website (https://higress.cn/en/)
- Simplify description to focus on key features
- Fix typo in the description

Change-Id: I5f1869d5cfbcc04674b4375fd82f4bf34b303280
Co-developed-by: Cursor <[email protected]>

Author: johnlanni

docs/versioned/install/README.md

@@ -101,6 +101,13 @@ If you don't have an ingress that meets the requirements, Knative provides [net-
 
     The Kubernetes [Gateway API](https://kubernetes.io/docs/concepts/services-networking/gateway/) (beta).
 
+- Higress (Third-party integration)
+
+     [Higress](https://higress.cn/en/) provides enhanced traffic governance, authentication, WAF protection, and observability for Knative services with WASM plugin extensibility. See [Higress: A Best Practice for Knative Ingress Gateway](https://www.alibabacloud.com/blog/higress-a-best-practice-for-knative-ingress-gateway_600549).
+    
+    !!! note
+        This integration is not managed by the Knative community.
+
 ### Messaging plugins
 
 Knative has default lightweight in-memory messaging implementation if you don't already have a solution.