[Don't merge] Testing version.

* Enable sidecar sender.
* Use new metrics in libdatadog.

Author: hoolioh

ext/configuration.h

@@ -186,7 +186,7 @@ enum ddtrace_sampling_rules_format {
 
 #ifndef _WIN32
 #define DD_CONFIGURATION \
-    CONFIG(BOOL, DD_TRACE_SIDECAR_TRACE_SENDER, "false", .ini_change = zai_config_system_ini_change) \
+    CONFIG(BOOL, DD_TRACE_SIDECAR_TRACE_SENDER, "true", .ini_change = zai_config_system_ini_change) \
     DD_CONFIGURATION_ALL
 #else
 #define DD_CONFIGURATION DD_CONFIGURATION_ALL