adding K8s page to subnav (#11467)

* adding K8s page to subnav

per request from HLT, updating use case tab to lead to K8s page instead of service mesh.

* Update subnav.js

website/data/subnav.js

@@ -15,6 +15,10 @@ export default [
         text: 'Multi-Platform Service Mesh',
         url: '/use-cases/multi-platform-service-mesh',
       },
+      {
+        text: 'Consul on Kubernetes',
+        url: '/consul-on-kubernetes',
+      },
     ],
   },
   {