Option to set priorityClassName in helm chart for the deployment and stafulset

# Description
add values to the helm chart to set priorityClassName to postee statefulset and postee-ui deployment

# Use Case
i would like to be able to set the priorityClassName on the statefulset and deployment resources using the helm chart values
so i dont have to patch the resources with kustomize
# Acceptance Criteria

Inspect the Helm chart values and the templates for the Postee StatefulSet and postee-ui Deployment. Render the chart with priorityClassName values set for both resources and verify that the generated manifests contain those values without requiring a Kustomize patch.

Written by the indexing model from the issue text.