OCPBUGS-8892# Add pd-balanced to sc for gcp pd

Author: Lisa Pettyjohn

modules/persistent-storage-csi-gcp-pd-storage-class-ref.adoc

@@ -14,7 +14,9 @@ The GCP PD CSI driver uses the `csi.storage.k8s.io/fstype` parameter key to supp
 |===
 |Parameter  |Values  |Default  |Description
 
-|`type` | `pd-ssd` or `pd-standard` | `pd-standard` | Allows you to choose between standard PVs or solid-state-drive PVs.
+|`type` | `pd-ssd`, `pd-standard`, or `pd-balanced` | `pd-standard` | Allows you to choose between standard PVs or solid-state-drive PVs.
+
+The driver does not validate the value, thus all the possible values are accepted.
 |`replication-type`| `none` or `regional-pd` | `none` | Allows you to choose between zonal or regional PVs.
 |`disk-encryption-kms-key` | Fully qualified resource identifier for the key to use to encrypt new disks. | Empty string | Uses customer-managed encryption keys (CMEK) to encrypt new disks.
 |===