Add the AWS SDK user agent when available

This partially reverts the previous behavior
and always adds the AWS SDK user agent when the communication
goes through the SDK, to enrich the user agent string.

osquery/utils/aws/aws_util.cpp

@@ -346,10 +346,11 @@ std::shared_ptr<Aws::Http::HttpResponse> OsqueryHttpClient::MakeRequest(
   http::Request req(url);
 
   for (const auto& requestHeader : request.GetHeaders()) {
-    /* We don't want to set the AWS SDK user agent, lets skip it
-       and let the HTTP client use its default */
-    if (!boost::iequals(requestHeader.first, "User-Agent")) {
-      req << http::Request::Header(requestHeader.first, requestHeader.second);
+    // Prepend the osquery user agent to the AWS SDK agent
+    if (boost::iequals(requestHeader.first, "User-Agent")) {
+      req << http::Request::Header(
+          requestHeader.first,
+          FLAGS_http_user_agent + " " + requestHeader.second);
     }
   }