[BUG][AZURE] Flag delete_os_disk_on_termination has no effect when removing cluster

[cicharka]

Describe the bug
In configuration of virtual-machines there is flag delete_on_termination set to false, but it doesn't have effect during cluster removal (epicli delete) and all of the OS disks are removed anyway. Also, when using similar flag for data disk (delete_data_disks_on_termination), it has no effect.

How to reproduce

1. execute epicli apply ...
2. execute epicli delete ... on that build

Expected behavior
When setting delete_on_termination flag to false (which is default) OS disks should not be removed during epicli delete.

Config files
Any config

Environment

• Cloud provider: Azure
• OS: Ubuntu 20.04.3 LTS

epicli version: [epicli --version]

• 2.0.0dev
• all of the previous versions that use that flag

Additional context
On AWS this flag can preserve disks from being removed when removing cluster with epicli delete.
According to this comment it is because deletion of whole Resource Group.

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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
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• Feature has automated tests
• Automated tests passed (QA pipelines)
  • apply
  • upgrade
  • backup/restore
• Idempotency tested
• All conversations in PR resolved

[cicharka]

Todo:

• extend warning prompted during epicli delete
• remove delete_on_termination flag from epi schema and terraform vm definitions for Azure
• update documentation (inform about behavior during removal)