[Feature] Allow setting priorityclass of components

[ColonelBundy]

Is this a BUG REPORT or FEATURE REQUEST?:
Feature

What happened:
Portworx pods were evicted due to it's lower priroityclass

What you expected to happen:
Being able to set the priorityclass of portworx components to prevent eviction.

Today all the components have no priorityclass set other than the default but the preemptionPolicy is set to PreemptLowerPriority which is good but it does not hinder eviction completely. I would very much like to be able to specify our own priorityclass and handle this on our own.