add external uri field to config

We are not ready to use this value just yet, but this change keeps the config
definition synchronized so that we can use the latest version.

spectator/config.h

@@ -18,7 +18,8 @@ class Config {
 
   Config(std::map<std::string, std::string> c_tags, int read_to_ms,
          int connect_to_ms, int batch_sz, int freq_ms, int exp_freq_ms,
-         int meter_ttl_ms, size_t age_gauge_limit, std::string publish_uri)
+         int meter_ttl_ms, size_t age_gauge_limit, std::string publish_uri,
+         std::string external_publish_uri)
       : common_tags{std::move(c_tags)},
         read_timeout{absl::Milliseconds(read_to_ms)},
         connect_timeout{absl::Milliseconds(connect_to_ms)},
@@ -27,7 +28,8 @@ class Config {
         expiration_frequency{absl::Milliseconds(exp_freq_ms)},
         meter_ttl{absl::Milliseconds(meter_ttl_ms)},
         age_gauge_limit{age_gauge_limit},
-        uri{std::move(publish_uri)} {}
+        uri{std::move(publish_uri)},
+        external_uri{std::move(external_publish_uri)} {}
   std::map<std::string, std::string> common_tags;
   absl::Duration read_timeout;
   absl::Duration connect_timeout;
@@ -37,6 +39,7 @@ class Config {
   absl::Duration meter_ttl;
   size_t age_gauge_limit{};
   std::string uri;
+  std::string external_uri;
   bool verbose_http = false;
   bool status_metrics_enabled = true;