Update User Guide and Admin links to point to new resources. (#3438)

* Update links to outdated user-guide and admin docs

* Add script for updating outdated links.

* Update regex to include init-containers file.

* Pull upstream, rewrite links in and to namespaces walkthrough.

docs/tutorials/clusters/multiple-schedulers.md

@@ -52,9 +52,9 @@ gcloud docker -- push gcr.io/my-gcp-project/my-kube-scheduler:1.0
 
 Now that we have our scheduler in a container image, we can just create a pod
 config for it and run it in our Kubernetes cluster. But instead of creating a pod
-directly in the cluster, let's use a [Deployment](/docs/user-guide/deployments/)
-for this example. A [Deployment](/docs/user-guide/deployments/) manages a
-[Replica Set](/docs/user-guide/replicasets/) which in turn manages the pods,
+directly in the cluster, let's use a [Deployment](/docs/concepts/workloads/controllers/deployment/)
+for this example. A [Deployment](/docs/concepts/workloads/controllers/deployment/) manages a
+[Replica Set](/docs/concepts/workloads/controllers/replicaset/) which in turn manages the pods,
 thereby making the scheduler resilient to failures. Here is the deployment
 config. Save it as `my-scheduler.yaml`: