feat(csi): make plugin directory configurable

[sysakdemy]

Summary

This PR makes the CSI plugin directory configurable in the Helm chart instead of hardcoding csi-plugins.

A new Helm value is introduced:

• pluginDir (default: csi-plugins)

The CSI driver templates now use:

{{ .Values.kubeletDir }}/{{ .Values.pluginDir }}/{{ include "driverName" . }}/

This preserves the current default behavior while allowing OpenShift/OKD environments to use plugins.

Closes #229

Why

On OKD/OpenShift 4, the kubelet plugin directory is typically:

{{ .Values.kubeletDir }}/plugins/

Using the hardcoded csi-plugins path prevents CSI driver registration, which can lead to:

• csi-node CrashLoopBackOff
• PVC mount failures
• workload startup failures due to missing registered CSI driver

Changes

• Added pluginDir to values.yaml with default value csi-plugins
• Replaced hardcoded csi-plugins paths in CSI-related templates with {{ .Values.pluginDir }}
• Updated chart documentation (README values table) to include pluginDir

Backward compatibility

• ✅ Default behavior is unchanged (pluginDir: csi-plugins)
• ✅ Existing deployments that do not set pluginDir continue to work as before

How to use

Default (no change required):

helm upgrade --install juicefs-csi . \
  --namespace kube-system

OpenShift/OKD:

helm upgrade --install juicefs-csi . \
  --namespace kube-system \
  --set pluginDir=plugins

Validation

• Rendered templates with default values and confirmed csi-plugins is still used
• Rendered templates with --set pluginDir=plugins and confirmed plugins is used in:
  • CSI plugin hostPath
  • DRIVER_REG_SOCK_PATH
• Verified chart templates remain valid

[sysakdemy]

Hi, could you please review this PR when you have time?
This change makes CSI plugin directory configurable for OKD/OpenShift compatibility.
Thanks!