Create a Dedicated Website for Kubeflow Spark Operator

### What feature you would like to be added?

Based on the direction set by the [Kubeflow Trainer project](https://github.com/kubeflow/trainer/issues/3255), this issue is to create a dedicated documentation website for the Kubeflow Spark Operator using the same pattern and tech stack.

Since migrating the Spark Operator from Google Cloud to Kubeflow in 2024, the project has seen significant community growth — with active contributions from Red Hat, multiple production deployments at scale, and increasing adoption from organizations like Red Hat, Salesforce, Airbnb, Pinterest, Fruitstand, Apple, OpenAI and Autodesk.

Benefits:

- **Docs co-located with source code** — making it easier to keep documentation up to date with code changes
- **Release-aligned documentation** — documentation updates can follow the Spark Operator's release cycle more closely
- **Clear project identity** — a dedicated website clearly positions the Spark Operator as a distinct sub-project within the broader Kubeflow ecosystem, similar to how Kubernetes SIGs projects have their own dedicated websites
- **Better onboarding experience** — new users and contributors can find getting started guides, API references and migration guides in one place
- **Community visibility** — showcase adopters, community calls, and contribution guidelines

We can follow the same approach as Kubeflow Trainer by creating a redirect from the main kubeflow.org website.

### References
- [Kubeflow Trainer dedicated website proposal](https://github.com/kubeflow/trainer/issues/3255)
- [Kubeflow Spark Operator repository](https://github.com/kubeflow/spark-operator)
- [Spark Operator announcement blog post](https://blog.kubeflow.org/operators/2024/04/15/kubeflow-spark-operator.html)

Looking forward to feedback and suggestions.

/cc @kubeflow/wg-data-leads

/cc @andreyvelich

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