chore(chart): add image_registry default value

Author: jianxiaoguo

charts/passport/values.yaml

@@ -1,7 +1,7 @@
 org: "drycc"
 image_pull_policy: "Always"
 image_tag: "canary"
-image_registry: ""
+image_registry: "docker.io"
 # Set passport deployment replicas
 replicas: 1
 # limits_cpu: "100m"
@@ -71,4 +71,4 @@ global:
   platform_domain: ""
   # Whether cert_passport is enabled to automatically generate passport certificates
   cert_passport_enabled: "true"
-  passport_location: "on-cluster"
+  passport_location: "on-cluster"