[main] HttpUtils: make setUserAgent static

src/main/java/io/gitlab/jfronny/commons/HttpUtils.java

@@ -62,7 +62,7 @@ public class HttpUtils {
             })
             .build();
 
-    public void setUserAgent(String hostname) {
+    public static void setUserAgent(String hostname) {
         if (hostname == null || hostname.isEmpty()) throw new IllegalArgumentException("Hostname cannot be empty");
         HttpUtils.userAgent = hostname;
     }