Add HPA / VPA scenario to PDB examples

**This is a Feature Request**

The [Think about how your application reacts to disruptions](https://kubernetes.io/docs/tasks/run-application/configure-pdb/#think-about-how-your-application-reacts-to-disruptions) section in [configure-pdb](https://kubernetes.io/docs/tasks/run-application/configure-pdb) covers some scenarios. I'd like to add an entry for workloads autoscaled by HPA or VPA, recommending `maxUnavailable` over `minAvailable`.
When `minAvailable` is set as an absolute number and HPA scales the replicas below that value, allowed Disruptions stays at 0, which blocks drain. `maxUnavailable` (>=1) avoids this because it always allows at least one eviction as long as the value is 1 or greater, regardless of the current replica count.

**Why is this needed**

HPA is widely used, and PDB is recommended for production workloads. The interaction of these two is not documented anywhere.

**Comments**

I encountered this issue in a prod environment and think this guidance can belong to the official docs.
I'd like to hear whether this documentation has enough value or not.

Start with the “Think about how your application reacts to disruptions” section in the configure-pdb documentation linked in the issue, and review its existing scenarios. Add an HPA/VPA scenario explaining why maxUnavailable is preferable to an absolute minAvailable value, then verify the guidance is clear and consistent with the surrounding PDB examples.

Written by the indexing model from the issue text.