Add nullability annotations to smoke-test/spring-boot-smoke-test-reactive-oauth2-resource-server

See gh-46587

smoke-test/spring-boot-smoke-test-reactive-oauth2-resource-server/src/main/java/smoketest/oauth2/resource/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+@NullMarked
+package smoketest.oauth2.resource;
+
+import org.jspecify.annotations.NullMarked;