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* Update links to outdated user-guide and admin docs

* Add script for updating outdated links.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/tasks/debug-application-cluster/debug-init-containers.md

@@ -23,8 +23,8 @@ Init Containers.
 {% capture prerequisites %}
 
 * You should be familiar with the basics of
-  [Init Containers](/docs/user-guide/pods/init-container/).
-* You should have a [Pod](/docs/user-guide/pods/) you want to debug that uses
+  [Init Containers](/docs/concepts/abstractions/init-containers/).
+* You should have a [Pod](/docs/concepts/workloads/pods/pod/) you want to debug that uses
   Init Containers. The example command lines below refer to the Pod as
   `<pod-name>` and the Init Containers as `<init-container-1>` and
   `<init-container-2>`.