Arrange the Extending Kubernetes section in the Concepts TOC (#8569)

* Left nav for Extending Kubernetes

* Redirect moved topics. Remove extraneous directory.

content/en/docs/concepts/api-extension/_index.md

@@ -1,5 +0,0 @@
----
-title: "Extending the Kubernetes API"
-weight: 20
----
-

content/en/docs/concepts/extend-kubernetes/_index.md

@@ -0,0 +1,3 @@
+---
+title: Extending Kubernetes
+---

content/en/docs/concepts/extend-kubernetes/api-extension/_index.md

@@ -0,0 +1,4 @@
+---
+title: Extending the Kubernetes API
+weight: 20
+---

content/en/docs/concepts/extend-kubernetes/api-extension/apiserver-aggregation.md

@@ -5,6 +5,7 @@ reviewers:
 - cheftako
 - chenopis
 content_template: templates/concept
+weight: 10
 ---
 
 {{% capture overview %}}

content/en/docs/concepts/extend-kubernetes/api-extension/custom-resources.md

@@ -4,6 +4,7 @@ reviewers:
 - enisoc
 - deads2k
 content_template: templates/concept
+weight: 20
 ---
 
 {{% capture overview %}}

content/en/docs/concepts/extend-kubernetes/compute-storage-net/_index.md

@@ -0,0 +1,4 @@
+---
+title: Compute, Storage, and Networking Extensions
+weight: 30
+---

content/en/docs/concepts/extend-kubernetes/compute-storage-net/device-plugins.md

@@ -3,6 +3,7 @@ reviewers:
 title: Device Plugins
 description: Use the Kubernetes device plugin framework to implement plugins for GPUs, NICs, FPGAs, InfiniBand, and similar resources that require vendor-specific setup.
 content_template: templates/concept
+weight: 20
 ---
 
 {{< feature-state state="beta" >}}

content/en/docs/concepts/extend-kubernetes/compute-storage-net/network-plugins.md

@@ -4,6 +4,7 @@ reviewers:
 - freehan
 - thockin
 title: Network Plugins
+weight: 10
 ---
 
 {{< toc >}}

content/en/docs/concepts/extend-kubernetes/extend-cluster.md

@@ -6,6 +6,7 @@ reviewers:
 - cheftako
 - chenopis
 content_template: templates/concept
+weight: 10
 ---
 
 {{% capture overview %}}

content/en/docs/concepts/extend-kubernetes/service-catalog.md

@@ -3,6 +3,7 @@ title: Service Catalog
 reviewers:
 - chenopis
 content_template: templates/concept
+weight: 40
 ---
 
 {{% capture overview %}}