Add option to use Secrets Store CSI driver to inject secrets into KBS file store

[bpradipt]

A secret store CSI driver can be used to inject the secrets into the KBS file store. See the following blog describing how Azure Key Vault Storage is used to inject secrets into the KBS file store - https://confidentialcontainers.org/docs/key-broker-service/kbs-backed-by-akv/
Similar approach can be followed with Hashicorp vault: https://developer.hashicorp.com/vault/docs/platform/k8s/csi

This issue is to track adding support in the operator for the same

Ref: https://secrets-store-csi-driver.sigs.k8s.io/getting-started/usage.html

[bpradipt]

This will be mostly documentation.
cc @lmilleri