[Backport release-1.6] fix(platform): accept the container gpu-operator variant in iaas - #5073

The cozystack.gpu-operator PackageSource ships three variants: default,
vgpu and container. The iaas bundle's variant guard accepted only the
first two, so selecting container failed the render on a value the
package ships, values-container.yaml configures deliberately, and the
variant bats suite already covers.

The exclusion was coherent when it was written and stopped being so
immediately. The container variant and the guard landed within minutes
of each other from parallel branches, neither an ancestor of the other,
variant first. Until the guard, the bundle hardcoded the default variant
and container was selected by hand-crafting a Package CR, so leaving it
out of a bundle-side list cost nothing. The guard then made the bundle
the variant owner and closed that route without noticing it was one; its
comment describes itself as typo protection and names passthrough as the
example typo.

The KubeVirt side is not a bare allowlist edit. The container variant
serves GPUs to pods through the device plugin and runs no VM-facing
GPU stack: sandboxWorkloads and vfioManager are both off and the host
driver stays bound. Both KubeVirt-side pieces the bundle wires are
VM-facing — the HostDevices feature gate advertises a capability such
a node cannot serve, and permittedHostDevices lists resources no
sandbox device plugin registers there. Both are now emitted only for
default and vgpu, and container yields the gpu-operator Package with
the kubevirt component untouched.

Comments and docs that described the KubeVirt mirroring as
unconditional on variant, or the container variant as unmerged and
unavailable, are corrected to match.

Assisted-by: LLM
Signed-off-by: Aleksei Sviridkin <[email protected]>
(cherry picked from commit 6e8566a)

Adapted for release-1.6: the conflict in packages/core/platform/values.yaml
sat in the kubevirt block, where main also carries a disabledFeatureGates
key that this branch does not have. The branch's kubevirt.migrations
setting is kept as it was and only the reworded gpu block comment is
taken from the original.

Signed-off-by: Myasnikov Daniil <[email protected]>