DOC: errors in K8s upgrade documentation

[Elisamara Aoki Gonçalves]

Brief Description
-----------------
‘The default version on a fresh install will be Kubernetes 1.21.8, while on an upgrade from stx8 it will be 1.18.1. You will need to upgrade Kubernetes to each version up to 1.21.8 in order to be ready to upgrade to the next version of stx.’

This information is incorrect. In stx8 the default for a fresh install will be 1.24.4, while on an upgrade from stx8 it will be 1.21.8 and on an upgrade from stx7 it will be 1.23.1.

'Note: Kubernetes version upgrade is currently only supported for hosts with worker function. Any attempt to modify the controller or storage apply type is rejected.'

This is incorrect, the intent is to say that the "-controller-apply-type" and "storage-apply-type" options are not applicable to K8s upgrades, only the "worker-apply-type" option applies. Also, AIO nodes have the worker function but also the controller function, and the "-worker-apply-type" option does not apply to them. It only applies to nodes that are only worker nodes.

So that note should read something like:
"Note: Setting the Kubernetes version upgrade apply type is currently only supported for hosts with only the worker function. Any attempt to modify the controller or storage apply type is rejected."
 The overall orchestrated K8s version upgrade is very much supported for controller nodes, since that is where the K8s control plane runs.

Severity
--------

<Minor: System/Feature is usable with minor issue>

[Elisamara Aoki Gonçalves (egoncalv)]

Update applied to master and stx8:
https://review.opendev.org/c/starlingx/docs/+/886212
https://review.opendev.org/c/starlingx/docs/+/886952