[spike] plan kubernetes upgrade

[mkyc]

• choose which version we are upgrading to, probably not the latest but the latest stable
• check changelogs about what was deprecated
• check upgrade guides https://kubernetes.io/docs/tasks/administer-cluster/cluster-upgrade/ - is there only incremental upgrade possible?
• check changes in our code since Upgrade Kubernetes to v1.18.6 #1501
• check support policies https://kubernetes.io/releases/version-skew-policy/
• if there is enough time, try to upgrade manually to find pitfalls
• create result tasks and assign to "Kubernetes upgrade" epic

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DoD checklist

• Reader is able to understand the results of spike
• The results of the spike are presented in a table (to show simply what are compared or researched parameters) / not applicable
• Each value / cell in the results table is described more deeply below
• Demo of the spike (automated as much as possible)
• Design doc updated

[atsikham]

The result of this spike is combining of related tasks into one Epic - https://app.zenhub.com/workspaces/epiphany-platform-5ef9d3c749afc20019782391/issues/epiphany-platform/epiphany/2620

Besides existing tasks, new ones were created:

#2657 - Add additional preflight check for upgrade
#2093 - Renamed to "Upgrade Kubernetes to 1.19.x"
#2658 - Upgrade Kubernetes to 1.20.x
#2659 - Upgrade Kubernetes to 1.21.x
#2660 - Upgrade Kubernetes to 1.22.x
#2661 - Update documentation
#2662 - Refactor K8s roles - may be done later and even in the scope of another epic

Upgrades should be incremental, so there is a separate task for each version. Moreover, it will allow us test them separately, find issues on earlier stages and release versions that we are able to complete upgrade for.

[mkyc]

Thanks @atsikham. LGTM.