Fix: Disable dynamic plugin cache PVC by default

[Fortune-Ndlovu]

Description of the change

This PR disables the dynamic plugin cache PVC by default in the RHDH Helm Chart.

Changes

• Introduces dynamicPlugins.cache.ephemeral to control storage behavior.
• If ephemeral: true (default), the PVC is not created, and emptyDir is used.
• If ephemeral: false, the PVC is created to persist cached plugins.
• PVC creation logic is now handled entirely in pvcs.yaml, avoiding if-else in values.yaml.

How to Test

1. Deploy with ephemeral: true (default) and verify no PVC is created:

   helm upgrade --install rhdh-backstage charts/backstage --namespace rhdh --set dynamicPlugins.cache.ephemeral=true
   oc get pvc -n rhdh  # No dynamic-plugins-root PVC should be present
   
   

Existing or Associated Issue(s)

https://issues.redhat.com/browse/RHIDP-5569

Additional Information

Checklist

• Chart version bumped in Chart.yaml according to semver.
• Variables are documented in the values.yaml and added to the README.md. The pre-commit utility can be used to generate the necessary content. Use pre-commit run -a to apply changes.
• JSON Schema template updated and re-generated the raw schema via pre-commit hook.
• List tests pass for Chart using the Chart Testing tool and the ct lint command.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud