util: add vaultAuthNamespace option for Vault KMS

The new `vaultAuthNamespace` configuration parameter can be set to the
Vault Namespace where the authentication is setup in the service. Some
Hashicorp Vault deployments use sub-namespaces for their users/tenants,
with a 'root' namespace where the authentication is configured. This
requires passing of different Vault namespaces for different operations.

Example:
 - the Kubernetes Auth mechanism is configured for in the Vault
   Namespace called 'devops'
 - a user/tenant has a sub-namespace called 'devops/website' where the
   encryption passphrases can be placed in the key-value store

The configuration for this, then looks like:

    vaultAuthNamespace: devops
    vaultNamespace: devops/homepage

Note that Vault Namespaces are a feature of the Hashicorp Vault
Enterprise product, and not part of the Open Source version. This
prevents adding e2e tests that validate the Vault Namespace
configuration.

Signed-off-by: Niels de Vos <ndevos@redhat.com>
(cherry picked from commit f2d5c2e0df)

examples/kms/vault/kms-config.yaml

@@ -52,6 +52,30 @@ data:
               }
           }
       },
+      "vault-tenant-sa-ns-test": {
+          "encryptionKMSType": "vaulttenantsa",
+          "vaultAddress": "http://vault.default.svc.cluster.local:8200",
+          "vaultBackend": "kv-v2",
+          "vaultBackendPath": "shared-secrets",
+          "vaultAuthNamespace": "devops",
+          "vaultNamespace": "devops/homepage",
+          "vaultTLSServerName": "vault.default.svc.cluster.local",
+          "vaultCAVerify": "false",
+          "tenantConfigName": "ceph-csi-kms-config",
+          "tenantSAName": "ceph-csi-vault-sa",
+          "tenants": {
+              "webservers": {
+                  "vaultAddress": "https://vault.example.com",
+                  "vaultAuthNamespace": "webservers",
+                  "vaultNamespace": "webservers/homepage",
+                  "vaultCAVerify": "true"
+              },
+              "homepage-db": {
+                  "vaultNamespace": "devops/homepage/database",
+                  "tenantSAName": "storage-encryption-sa"
+              }
+          }
+      },
       "secrets-metadata-test": {
           "encryptionKMSType": "metadata"
       },