[Enhancement] support priorityClassName (#642)

[jenwitteng]

Description

add priorityClassName

Related Issue(s)

#642

Checklist

For operator, please complete the following checklist:

• run make generate to generate the code.
• run golangci-lint run to check the code style.
• run make test to run UT.
• run make manifests to update the yaml files of CRD.

For helm chart, please complete the following checklist:

• make sure you have updated the values.yaml
  file of starrocks chart.
• In scripts directory, run bash create-parent-chart-values.sh to update the values.yaml file of the parent
  chart( kube-starrocks chart).

[CLAassistant]

All committers have signed the CLA.