implement headers() in jetty12 request (#2140)

Author: obenkenobi

instrumentation/jetty-12/src/main/java/com/nr/agent/instrumentation/jetty12/JettyRequest.java

@@ -34,6 +34,15 @@ public String getHeader(String name) {
         return request.getHeaders().get(name);
     }
 
+    @Override
+    public List<String> getHeaders(String name) {
+        Enumeration<String> headers = request.getHeaders().getValues(name);
+        if (headers == null) {
+            return Collections.emptyList();
+        }
+        return Collections.list(headers);
+    }
+
     @Override
     public String getRequestURI() {
         return request.getHttpURI().getPath();
@@ -88,4 +97,5 @@ public String getCookieValue(String name) {
         }
         return null;
     }
+
 }