Add license header to every source file

[leggerf]

Example of license (look at the README):

https://github.com/indico/indico-plugins-cern

see source for example:

https://github.com/indico/indico-plugins-cern/blob/master/run-tests.sh

 Copyright (C) 2014 - 2022 CERN

 The CERN Indico plugins are free software; you can redistribute
 them and/or modify them under the terms of the MIT License; see
 the LICENSE file for more details.

We should modify CERN -> INFN

[gabrielefronze]

I suggest AGLP. Have a look: https://www.gnu.org/licenses/agpl-3.0.en.html

[leggerf]

we need further discussion of GPL vs AGPL

[leggerf]

We're going for MIT. We should also properly treat files from phoronix, which is released under GPL

[leggerf]

On hold till we have feedback from INFN

[leggerf]

add this header to each source file:

// Copyright (c) 2021-2022 Istituto Nazionale di Fisica Nucleare // SPDX-License-Identifier: MIT