Add license in Dockerfile

Update the license format in Dockerfile as an example. These two lines need to be inserted in all the file in the project repo

.devcontainer/Dockerfile

+# Copyright 2018-2022 Istituto Nazionale di Fisica Nucleare
+# SPDX-License-Identifier: EUPL-1.2
+
 FROM centos:7
 
 # Allow customization of build user ID and name