Add Volume Selectors when binding PVC

RabbitMQ Chart already has this feature.

https://github.com/helm/charts/blob/master/stable/rabbitmq/values.yaml#L300-L307

```
persistence:
storageClass: "manual"
selector:
matchLabels:
app: rabbitmq
size: {{replicaSize}}
```

Use the linked RabbitMQ values.yaml persistence example as the reference entry point, then locate the Vault chart values and PVC template that handle persistence. Confirm that selector values can be supplied through the chart and appear in the rendered PVC, with the existing chart checks passing.

Written by the indexing model from the issue text.