Update install-kubectl.md to use tabs for the different Operating Systems (#26682)

* top-level tags and change to included files

* revert content to main windows page

* include gcloud and update toc

* add leading blank line

* add text to avoid YAML error from Netlify

* remove YAML delimiter error

* removed redundant weight key

* add front matter and toc shortcode

* test to see if toc is fixed in included page

* update macos toc to show difference

* use static toc instead of shortcode

* uniqueness for gcloud install headers

* Move to model suggested in https://github.com/kubernetes/website/pull/26682#discussion_r585091797

* correct link to included/install-kubectl-gcloud.md

* correction of links to per-OS pages

* try a different way to use path to per-OS links

* correction of brainfart

* remove .md from link destination for per-OS pages

* modify how auto-competion steps are displayed

* remove redundant file

* correction of include - change % to <

* remove closing tag as not needed

* try and hide this directory from the ToC on the left

* remove erroneous "include="

* addressing feedback: https://github.com/kubernetes/website/pull/26682#discussion_r586325123

* addressing feedback: https://github.com/kubernetes/website/pull/26682#discussion_r586326346

* addressing feedback: https://github.com/kubernetes/website/pull/26682#discussion_r586326604

* addressing feedback: https://github.com/kubernetes/website/pull/26682#discussion_r586327212

* https://github.com/kubernetes/website/pull/26682#discussion_r586327856

* consistent verb usage as per feedback: https://github.com/kubernetes/website/pull/26682#discussion_r586328497

* update redirects as existing page is being deleted

static/_redirects

@@ -275,7 +275,8 @@
 /docs/tasks/job/work-queue-1/     /docs/concepts/workloads/controllers/job/ 301
 /docs/tasks/setup-konnectivity/setup-konnectivity/   /docs/tasks/extend-kubernetes/setup-konnectivity/ 301
 /docs/tasks/kubectl/get-shell-running-container/     /docs/tasks/debug-application-cluster/get-shell-running-container/ 301
-/docs/tasks/kubectl/install/     /docs/tasks/tools/install-kubectl/ 301
+/docs/tasks/kubectl/install/     /docs/tasks/tools/ 301
+/docs/tasks/tools/install-kubectl/     /docs/tasks/tools/ 301
 /docs/tasks/kubectl/list-all-running-container-images/     /docs/tasks/access-application-cluster/list-all-running-container-images/ 301
 /docs/tasks/manage-stateful-set/debugging-a-statefulset/     /docs/tasks/debug-application-cluster/debug-stateful-set/ 301
 /docs/tasks/manage-stateful-set/delete-pods/     /docs/tasks/run-application/delete-stateful-set/ 301