chore: add missing headers to files

DGCAVerifier/Utils/HCert/HCert+Certificate.swift

@@ -1,3 +1,21 @@
+/*
+ *  license-start
+ *  
+ *  Copyright (C) 2021 Ministero della Salute and all other contributors
+ *  
+ *  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
+ *  
+ *      http://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.
+*/
+
 //
 //  HCert+Certificate.swift
 //  Verifier