feat(gpu): model step 1 tenant entitlement and class entries #78

The provider needs to expose the GPU step 1 fields. The design is merged in cozystack/community#99.

Required for step 1

• Add Tenant gpu.vgpu to the resource and data source, including schema and expand/flatten handling. Cover explicit true, explicit false and omission without adding a provider-side default. The field comes from cozystack/cozystack#5008.
• Add className and count to the VMInstance and KubernetesNodes GPU schemas and expand/flatten handling. Preserve existing raw name entries and the upstream validation rules. Class entries come from cozystack/cozystack#5030. The GPUClass catalog is introduced in cozystack/cozystack#4998.
• Add round-trip and schema-coverage tests for these fields, and regenerate the resource and data-source documentation.

Later

No additional changes proposed here.