[SPARK-52295] Add pi-v1alpha1.yaml example

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR aims to add pi-v1alpha1.yaml example.

$ diff examples/pi.yaml examples/pi-v1alpha1.yaml
15c15
< apiVersion: spark.apache.org/v1beta1
---
> apiVersion: spark.apache.org/v1alpha1
18c18
<   name: pi
---
>   name: pi-v1alpha1

Why are the changes needed?

To give an example to support old versions.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Manual review because this is an example.

Was this patch authored or co-authored using generative AI tooling?

No.

[dongjoon-hyun]

Since this is an example, I'll merge this.

[dongjoon-hyun]

Merged to main.