Allow to set priority class to timescale StatefulSet

[may-cDev]

What is missing?
It would be nice to be able to set the priority class of our timescaledb pods.
https://kubernetes.io/docs/concepts/scheduling-eviction/pod-priority-preemption/

Why do we need it?
Kubernetes Priority classes help to manage the importance of Pods. By using Priority Classes one can define whcih pods should be evicted first in case of resource pressure. As in many environments the timescale database is a mission-critical part it makes sense to assign it a higher priority than to other pods.

Anything else we need to know?: