Respect system proxy settings in WebClient

HTTP(S) proxy settings are applied only in some specific cases when `configureSsl` is called with some non-null params.
They should be always used.

kafka-ui-api/src/main/java/com/provectus/kafka/ui/util/WebClientConfigurator.java

@@ -31,6 +31,10 @@ public class WebClientConfigurator {
 
   public WebClientConfigurator() {
     configureObjectMapper(defaultOM());
+    var httpClient = HttpClient
+        .create()
+        .proxyWithSystemProperties();
+    builder.clientConnector(new ReactorClientHttpConnector(httpClient));
   }
 
   private static ObjectMapper defaultOM() {