Expose `priorityClassName` in the intel-device-plugins-operator

[tiesmaster]

I'd like to be able to set the priorityClassName of the Deployment. I know you can set this via helm post renderers (and that's how I do that now), though, many helm charts allow you to set the priorityClassName, so I think it would be an useful addtion for the chart as well.

Shall I make a PR?

[mythi]

Sounds reasonable to me, a PR is OK. Note that the plugins have built-in templates the operator uses and priorityClassName is not set.