kube/redis: fix /data partition permissions

This has been encountered when introducing redis in our production
matrix deployment. /data partition is owned by root:root by default
otherwise.

Change-Id: Ic148ff25837c6e8da394a5124556481343ea2873

kube/redis.libsonnet

@@ -81,6 +81,8 @@ local kube = import "kube.libsonnet";
                     },
                     securityContext: {
                         runAsUser: 100,
+                        runAsGroup: 101,
+                        fsGroup: 101,
                     },
                 },
             },