Add whitespace after copyright header

Add an additional lines after the copyright header and before the
`package` declaration. This aligns with the style used by Spring
Framework.

Issue gh-8945

samples/boot/oauth2webclient/src/main/java/sample/OAuth2WebClientApplication.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package sample;
 
 import org.springframework.boot.SpringApplication;

samples/boot/oauth2webclient/src/main/java/sample/config/SecurityConfig.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package sample.config;
 
 import org.springframework.context.annotation.Bean;

samples/boot/oauth2webclient/src/main/java/sample/web/OAuth2WebClientController.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package sample.web;
 
 import org.springframework.stereotype.Controller;

samples/boot/oauth2webclient/src/main/java/sample/web/RegisteredOAuth2AuthorizedClientController.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package sample.web;
 
 import org.springframework.security.oauth2.client.OAuth2AuthorizedClient;