message: docs: clarify hc host default
  The default is actually the cluster name, not the ip
diff: @@ -61,8 +61,8 @@ message HealthCheck {
  message HttpHealthCheck {
  // The value of the host header in the HTTP health check request. If
  - // left empty (default value), the IP on behalf of which this health check is performed will be
  - // used.
  + // left empty (default value), the name of the cluster this health check is associated
  + // with will be used.
  string host = 1;
  // Specifies the HTTP path that will be requested during health checking. For example
  