docs/compute/virtual_hardware.md: add VideoConfig feature gate and video type override support

[dasionov]

What this PR does / why we need it:

This PR enhances the documentation around the VideoConfig feature by adding clear guidance and updates. It documents how to configure the VideoConfig feature gate, introduces an architecture-specific support table for video types, updates examples to use the correct video.type syntax, and adjusts the default video memory overhead from 16 MB to 32 MB for improved accuracy.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Related to kubevirt/enhancements#87

Special notes for your reviewer:

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• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
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Release note:

Add VideoConfig feature gate support to docs

[kubevirt-bot]

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[0xFelix]

Since it is upstream documentation, can you please refer to the corresponding HCO version instead?

[dasionov]

it's currently in main.. no actual release in upstream.

i think we can drop this part, and update the docs once we have formal release for that

what do you think?

I can add a TODO for that.

[0xFelix]

Sounds good

[0xFelix]

/lgtm