Update parameter reference docs

Signed-off-by: Stephan Austermühle <[email protected]>

Author: stephan2012

docs/reference/operator_parameters.md

@@ -425,7 +425,7 @@ configuration they are grouped under the `kubernetes` key.
   environment if they not if conflict with the environment variables generated
   by the operator. The WAL location (bucket path) can be overridden, though.
   The default is empty.
-  
+
 * **pod_environment_secret**
   similar to pod_environment_configmap but referencing a secret with custom
   environment variables. Because the secret is not allowed to exist in a
@@ -453,6 +453,15 @@ configuration they are grouped under the `kubernetes` key.
   non-root process, but requires a custom Spilo image. Note the FSGroup of a Pod
   cannot be changed without recreating a new Pod.
 
+* **pod_fs_group_change_policy**
+  Configure the `fsGroupChangePolicy` in the Pod `securityContext` to
+  avoid invalid volume permissions after `kubelet` restarts. See *[Configure volume permission and ownership change policy for Pods](https://kubernetes.io/docs/tasks/configure-pod-container/security-context/#configure-volume-permission-and-ownership-change-policy-for-pods)*
+  for details. If specified, valid options are `OnRootMismatch`
+  (change permissions and ownership if the permission and the
+  ownership of root directory does not match with expected permissions
+  of the volume) and `Always` (always change permission and ownership
+  of the volume when volume is mounted).
+
 * **spilo_privileged**
   whether the Spilo container should run in privileged mode. Privileged mode is
   used for AWS volume resizing and not required if you don't need that
@@ -552,7 +561,7 @@ effect, and the parameters are grouped under the `timeouts` key in the
 CRD-based configuration.
 
 * **PatroniAPICheckInterval**
-  the interval between consecutive attempts waiting for the return of 
+  the interval between consecutive attempts waiting for the return of
   Patroni Api. The default is `1s`.
 
 * **PatroniAPICheckTimeout**
@@ -750,7 +759,7 @@ grouped under the `logical_backup` key.
   is specified, no argument will be passed to `aws s3` command. Default: "AES256".
 
 * **logical_backup_s3_retention_time**
-  Specify a retention time for logical backups stored in S3. Backups older than the specified retention 
+  Specify a retention time for logical backups stored in S3. Backups older than the specified retention
   time will be deleted after a new backup was uploaded. If empty, all backups will be kept. Example values are
   "3 days", "2 weeks", or "1 month". The default is empty.