add missing license header

Author: ktoso

Samples/JExtractPluginSampleApp/src/main/java/com/example/swift/JExtractPluginSampleMain.java

@@ -1,3 +1,17 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
 package com.example.swift;
 
 import org.swift.swiftkit.SwiftKit;