[FEATURE REQUEST] Implement control plane downscale

[atsikham]

Is your feature request related to a problem? Please describe. This request is the result of #1497 spike. At the moment Epiphany has no ability to scale down control plane nodes, this ability should be added.

Describe the solution you'd like When count of k8s control plane nodes is decreased in config file and new configuration applied, all necessary work, such as kubeadm reset should be done before node removal by Terraform. Also it should be possible to revert HA promotion.

Describe alternatives you've considered No

Additional context

• Documentation about scaling process should be updated.
• Should work for all cloud providers.

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DoD checklist

• Changelog
  • [ ] updated
  • [ ] not needed
• COMPONENTS.md
  • [ ] updated
  • [ ] not needed
• Schema
  • [ ] updated
  • [ ] not needed
• Backport tasks
  • [ ] created
  • [ ] not needed
• Documentation
  • [ ] added
  • [ ] updated
  • [ ] not needed
• [ ] Feature has automated tests
• [ ] Automated tests passed (QA pipelines)
  • [ ] apply
  • [ ] upgrade
  • [ ] backup/restore
• [ ] Idempotency tested
• [ ] All conversations in PR resolved
• [ ] Solution meets requirements and is done according to design doc
• [ ] Usage compliant with license