Support mounting certificate and private key in separate files

[vaibhav-gupt]

For a certificate, mount the private key and public key in separate files. Currently, CSI driver downloads the complete certificate and mounts it in a single file. This single file does not work with the non-Microsoft components. As they expect, key and cert to be provided as separate files. AKV CSI driver supports parsing AKV cert for k8s tls secret but not for the volume mounts.

EG. CSI driver can mount the three files : /certName, /certName.key, certName.cert for the below resource

apiVersion: secrets-store.csi.x-k8s.io/v1
kind: SecretProviderClass
metadata:
name: contour
namespace: projectcontour
spec:
provider: azure
parameters:
  usePodIdentity: "true"
  keyvaultName: "${KEYVAULT_NAME}"
  objects:  |
    array:
      - |
        objectName: certName
        objectType: secret
        objectVersion: ""
  tenantId: "${KEYVAULT_TENANT_ID}" 

We need to mount the cert & key in pem format in contour and envoy pods. Also pass the file paths in configuration.

Environment:

• Secrets Store CSI Driver version: (use the image tag): v1.0.0
• Azure Key Vault provider version: (use the image tag): v1.0.0
• Kubernetes version: (use kubectl version): 1.22
• Cluster type: (e.g. AKS, aks-engine, etc): AKS