Describe the feature:
Currently there is no way to add custom labels to pvc created by statefulsets for logstash helm chart

I propose functionality to modify helm templates in logstash to support adding custom labels to PVCs created by StatefulSet.
The functionality can be mostly copy-pasted from elasticsearch helm chat where this functionality is implemented already

Describe a specific use case for the feature:
In my organisation all K8s objects have custom labels on them which are used to control logging and alerting flows.
Simplest example is prom alerting rule for pvc to alert me when elastic pvc are about to run out of capacity (logstash, elasticsearch).