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

content/en/docs/tasks/tools/included/_index.md

@@ -0,0 +1,6 @@
+---
+title: "Tools Included"
+description: "Snippets to be included in the main kubectl-installs-*.md pages."
+headless: true
+toc_hide: true
+---