adds missing license header

shogun-proxy/src/main/java/de/terrestris/shogun/config/HttpProxyConfig.java

@@ -1,3 +1,19 @@
+/* SHOGun, https://terrestris.github.io/shogun/
+ *
+ * Copyright © 2021-present terrestris GmbH & Co. KG
+ *
+ * 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.txt
+ *
+ * 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.
+ */
 package de.terrestris.shogun.config;
 
 import de.terrestris.shogun.properties.KeycloakAuthProperties;