Feature: allow setting priorityClassName for the Renovate CronJob's pods

[cnd4]

Hello,

I think it would be nice to allow setting a priorityClassName in the Helm values when installing Renovate, so the pods created by the cron job would be low or high priority, depending on everyone's need. It can be useful in a cluster that have temporary pressure.

Thank in advance for considering this!

I don't when I will have some free time, otherwise it would have been a pleasure for me to make a PR.