feat(vm): validate cloud-init userdata

[hardcoretime]

Description

Cloud-init userdata in the virtual machine specification should not be empty or exceed 2048 KB.

Why do we need it, and what problem does it solve?

These changes are required to prevent the virtual machine from entering a pending status due to incorrect cloud-init userdata.

What is the expected result?

Webhook prevents virtual machine creation or update with incorrect cloud-init userdata and Provisioning Handler return an error if resource was created with invalidated data.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: vm
type: feature
summary: "Cloud-init userdata is now validated during virtual machine creation and updates."

[deckhouse-BOaTswain]

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