Updates HA kubeadm docs (#9066)

* Updates HA kubeadm docs

Signed-off-by: Chuck Ha <[email protected]>

* kubeadm HA - Add stacked control plane steps

* ssh instructions and some typos in the bash scripts

Signed-off-by: Chuck Ha <[email protected]>

* Fix typos and copypasta errors

* Fix rebase issues

* Integrate more changes

Signed-off-by: Chuck Ha <[email protected]>

* copyedits, layout and formatting fixes

* final copyedits

* Adds a sanity check for load balancer connection

Signed-off-by: Chuck Ha <[email protected]>

* formatting fixes, copyedits

* fix typos, formatting

Author: chuckha