message: Support lowercase http_proxy & https_proxy env
diff: @@ -111,7 +111,9 @@ impl ConfigLoader {
  if let Some(proxy) = nonempty(self.cluster.proxy_url.clone())
  .or_else(|| nonempty(std::env::var("HTTP_PROXY").ok()))
  + .or_else(|| nonempty(std::env::var("http_proxy").ok()))
  .or_else(|| nonempty(std::env::var("HTTPS_PROXY").ok()))
  + .or_else(|| nonempty(std::env::var("https_proxy").ok()))
  {
  Ok(Some(
  proxy
  