config timeout with CURLOPT_TIMEOUT_MS instead of CURLOPT_TIMEOUT for curl implementation

[wxl374]

When configure OtlpHttpExporter's timeout less than 1s, it will set to 0 for the use of CURLOPT_TIMEOUT(

opentelemetry-cpp/ext/include/opentelemetry/ext/http/client/curl/http_operation_curl.h

Line 189 in fd5a621

curl_easy_setopt(curl_, CURLOPT_TIMEOUT, http_conn_timeout_.count() / 1000);

), then never times out (sometimes limited by CURLOPT_LOW_SPEED_TIME). Why not use CURLOPT_TIMEOUT_MS instead？

[lalitb]

This is a good point. Would be good to see the libcurl version having CURLOPT_TIMEOUT_MS before supporting this. Moving this to issue to investigate further.