Add docs regarding Disk-only File-based Storage Instance Snapshot on KVM

[JoaoJandre]

Add docs regarding Disk-only File-based Storage Instance Snapshot on KVM

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📚 Documentation preview 📚: https://cloudstack-documentation--541.org.readthedocs.build/en/541/

[Copilot]

Pull Request Overview

This PR adds documentation for the new Disk-only File-based Storage Instance Snapshot feature on KVM hypervisors, introduced in CloudStack version 4.21. The documentation explains how this feature provides incremental disk-only instance snapshots for VMs on file-based storage systems with minimal downtime.

• Adds comprehensive documentation for the new KVM file-based storage instance snapshot strategy
• Explains the differences from existing storage-based instance snapshots
• Documents configuration options and limitations

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[weizhouapache]

lgtm

[sureshanaparti]

@blueorangutan docbuild

[blueorangutan]

@sureshanaparti a Jenkins job has been kicked to build the document. I'll keep you posted as I make progress.

[blueorangutan]

QA-Doc build preview: https://qa.cloudstack.cloud/builds/docs-build/pr/541. (QA-JID 408)