[Feature] Specify proxy auth explicitly when using system proxy (#300)

## Changes
<!-- Summary of your changes that are easy to understand -->
In certain cases, customers can use different ways to authenticate proxy
even when using the system proxy settings (basic, kerberos etc.). Hence,
post this change, the auth for system proxy can be done in different
ways and needs to be explicitly specified.

## Tests
<!-- How is this tested? -->
Tested on a proxy setup in VMs

---------

Co-authored-by: hectorcast-db <[email protected]>

Author: vikrantpuppala

databricks-sdk-java/src/main/java/com/databricks/sdk/core/utils/ProxyUtils.java

@@ -41,7 +41,7 @@ public static void setupProxy(ProxyConfig config, HttpClientBuilder builder) {
       proxyPort = Integer.parseInt(System.getProperty(protocol + ".proxyPort"));
       proxyUser = System.getProperty(protocol + ".proxyUser");
       proxyPassword = System.getProperty(protocol + ".proxyPassword");
-      proxyAuthType = ProxyConfig.ProxyAuthType.BASIC;
+      proxyAuthType = config.getProxyAuthType();
     }
     // Override system properties if proxy configuration is explicitly set
     if (config.getHost() != null) {