In T625 / D756 / f9e81e6d5fec, decision was to maintain in // two images,
one for PHP 5.6, one for PHP 7.1.

This choice doesn't seem interesting for PHP 8 as:

• Docker tags allow to select a precise version
• The Docker Hub build rules now allow to create a 1.2.3-novolume tag
• The nasqueron/php-cli image works just fine

It simplifies the maintenance operations and would avoid to have 4 images,
one for PHP CLI, three for nginx-php7-fpm.

To weld the repositories together, this change merges the docker-nginx-php7-fpm
main branch in this main branch.