docs(gpu): document the step 1 class catalog and configuration #784

The GPU step 1 rollout needs matching platform and guest documentation. The design is merged in cozystack/community#99.

Required for step 1

• Add platform gpu.vgpu to content/en/docs/next/operations/configuration/platform-package.md. It defaults to false and supplies the root tenant's entitlement; a child also needs its parent's entitlement. This comes from cozystack/cozystack#5008.
• Document platform gpu.resourceNames and its role in identifying GPU resource names, added in cozystack/cozystack#5030.
• Document the hoster's GPUClass catalog from cozystack/cozystack#4998. Cover VMInstance and KubernetesNodes class entries from cozystack/cozystack#5030, keeping raw name entries as the compatibility path.
• Document the guest license contract: the GPULICENSE disk, Linux token handling on a memory filesystem and license rotation at VMI restart. License delivery is added by cozystack/cozystack#5013. The VMI integration is in cozystack/cozystack#5030.

Later guide improvements

Operational follow-ups can cover rotation capacity and deadlines, real DLS/CLS rotation checks, maximum lease duration and offline leases, troubleshooting, and Windows token handling. These need their own verification and are not blockers for the step 1 reference. This issue does not commit to publishing every draft guide.