message: snapshotter: add blob_redirected_host config
  Previous commit introduced 'blob_redirected_host' config in nydus
  config, export this config in nydus-snapshotter as well.
diff: @@ -54,6 +54,7 @@ type DeviceConfig struct {
  Auth string `json:"auth,omitempty"`
  RegistryToken string `json:"registry_token,omitempty"`
  BlobUrlScheme string `json:"blob_url_scheme,omitempty"`
  + BlobRedirectedHost string `json:"blob_redirected_host,omitempty"`
  // OSS backend configs
  EndPoint string `json:"endpoint,omitempty"`
  