Allow setting priorityClassName on pods

[Javex]

I have a hardware device attached to my Home Assistant node, so it will only work on one particular node. To make sure that the scheduler makes room for HA (if other workloads have already been scheduled there), I created a priority class. I realised the template doesn't support this yet, so I've added an option.

If priorityClassName is set, this allows for a configuration where the scheduler evicts other pods and puts HA on the right node. Here's what that looks like for me (a snippet from my values.yaml):

priorityClassName: node-priority

nodeSelector:
  zigbee: "true"

Of course, there also needs to be a label on the node and the priority class needs to exist.

[pajikos]

Thank you @Javex