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/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/api-extension/apiserver-aggregation.md → 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/api-extension/custom-resources.md → 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/cluster-administration/device-plugins.md → 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/cluster-administration/network-plugins.md → 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/overview/extending.md → 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/service-catalog.md → 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 %}}

static/_redirects

@@ -72,17 +72,21 @@
 /docs/concepts/abstractions/init-containers/     /docs/concepts/workloads/pods/init-containers/ 301
 /docs/concepts/abstractions/overview/     /docs/concepts/overview/working-with-objects/kubernetes-objects/ 301
 /docs/concepts/abstractions/pod/     /docs/concepts/workloads/pods/pod-overview/ 301
+/docs/concepts/api-extension/apiserver-aggregation/     /docs/concepts/extend-kubernetes/api-extension/apiserver-aggregation/ 301
+/docs/concepts/api-extension/custom-resources/     /docs/concepts/extend-kubernetes/api-extension/custom-resources/ 301
 /docs/concepts/cluster/     /docs/concepts/cluster-administration/cluster-administration-overview/ 301
 /docs/concepts/cluster-administration/access-cluster/     /docs/tasks/access-application-cluster/access-cluster/ 301
 /docs/concepts/cluster-administration/audit/     /docs/tasks/debug-application-cluster/audit/ 301
 /docs/concepts/cluster-administration/authenticate-across-clusters-kubeconfig   /docs/tasks/access-application-cluster/authenticate-across-clusters-kubeconfig/ 301
 /docs/concepts/cluster-administration/cluster-management/     /docs/tasks/administer-cluster/cluster-management/ 301
 /docs/concepts/cluster-administration/configure-etcd/     /docs/tasks/administer-cluster/configure-upgrade-etcd/ 301
+/docs/concepts/cluster-administration/device-plugins/     /docs/concepts/extend-kubernetes/compute-storage-net/device-plugins/ 301
 /docs/concepts/cluster-administration/etcd-upgrade/     /docs/tasks/administer-cluster/configure-upgrade-etcd/ 301
 /docs/concepts/cluster-administration/federation-service-discovery/     /docs/tasks/federation/federation-service-discovery/ 301
 /docs/concepts/cluster-administration/guaranteed-scheduling-critical-addon-pods/     /docs/tasks/administer-cluster/guaranteed-scheduling-critical-addon-pods/ 301
 /docs/concepts/cluster-administration/master-node-communication/     /docs/concepts/architecture/master-node-communication/ 301
 /docs/concepts/cluster-administration/multiple-clusters/     /docs/concepts/cluster-administration/federation/ 301
+/docs/concepts/cluster-administration/network-plugins/     /docs/concepts/extend-kubernetes/compute-storage-net/network-plugins/ 301
 /docs/concepts/cluster-administration/out-of-resource/     /docs/tasks/administer-cluster/out-of-resource/ 301
 /docs/concepts/cluster-administration/resource-usage-monitoring /docs/tasks/debug-application-cluster/resource-usage-monitoring/ 301
 /docs/concepts/cluster-administration/sysctl-cluster/ /docs/tasks/administer-cluster/sysctl-cluster/ 301
@@ -96,8 +100,10 @@
 /docs/concepts/nodes/node/     /docs/concepts/architecture/nodes/ 301
 /docs/concepts/object-metadata/annotations/     /docs/concepts/overview/working-with-objects/annotations/ 301
 /docs/concepts/overview/     /docs/concepts/overview/what-is-kubernetes/ 301
+/docs/concepts/overview/extending/     /docs/concepts/extend-kubernetes/extend-cluster/ 301
 /docs/concepts/policy/container-capabilities/     /docs/tasks/configure-pod-container/security-context/#set-capabilities-for-a-container/ 301
 /docs/concepts/policy/security-context/     /docs/tasks/configure-pod-container/security-context/ 301
+/docs/concepts/service-catalog/     /docs/concepts/extend-kubernetes/service-catalog/ 301
 /docs/concepts/services-networking/networkpolicies/     /docs/concepts/services-networking/network-policies/ 301
 /docs/concepts/storage/etcd-store-api-object/     /docs/tasks/administer-cluster/configure-upgrade-etcd/ 301
 /docs/concepts/storage/volumes/emptyDirapiVersion/     /docs/concepts/storage/volumes/#emptydir/ 301