Implement vind smoke e2e provider

[michaelw]

Summary

Add a working E2E_CLUSTER_PROVIDER=vind implementation for the smoke e2e driver.

Context

PR #7 adds provider-based smoke e2e machinery with kind implemented and vind reserved as an explicit placeholder. The next step is to wire vind as another ephemeral target cluster provider.

Acceptance criteria

• E2E_CLUSTER_PROVIDER=vind make smoke creates an isolated ephemeral cluster using vind.
• The smoke driver uses a temporary kubeconfig and does not read or mutate the user's default kubeconfig.
• devspace deploy runs against the vind-created cluster.
• Existing install diagnostics pass against the vind cluster, or any provider-specific unsupported host integration is clearly skipped with evidence-backed reasoning.
• Cleanup deletes the ephemeral vind cluster by default.
• E2E_KEEP_CLUSTER=1 preserves the cluster and prints the kubeconfig/location needed for debugging.
• Documentation notes provider prerequisites and local usage.

Notes

• Keep the Go provider boundary introduced in PR Add smoke e2e workflow #7.
• Avoid long shell scripts; put nontrivial provider orchestration in Go.
• Consider the official setup-vind workflow behavior when designing CI support.