compute: add PCI topology and hotplug port reservation docs

[mhenriks]

Document the PCI topology versions (v1, v2, v3), how hotplug port reservation works, and upgrade behavior. Includes troubleshooting guidance for Windows VMs with offline disks after upgrading from KubeVirt 1.6/1.7 to versions with the v3 fix (1.6.4, 1.7.2, 1.8+).

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compute: add PCI topology and hotplug port reservation docs

[kubevirt-bot]

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[mhenriks]

cc @jean-edouard @vladikr @xpivarc

[kubevirt-bot]

There has been no activity on this PR for 45 days.
To protect limited CI resources, it has been automatically labelled 'stale'.
This PR will automatically rot after an additional 14 days of inactivity, and will be closed shortly after that.

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/lifecycle stale

[mhenriks]

/remove-lifecycle stale

[kubevirt-bot]

PR needs rebase.

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