Port tests to PHP 8.1 and PHPUnit 9.5

Summary:
PHPUnit provides now a assertStringContainsString method, while assertContains
is reserved for iterables.

All classes are put in a PSR-4 namespace, declared in composer.json.
PHPUnit will use the Composer autoloader to find them.

To help PHPUnit and phpcs to find code, the code is movd in two directories:

• utils/ → lib/Infrastructure/ for the Nasqueron\Infrastructure namespace
• (root) → tests/ for the Nasqueron\Infrastructure\ProductionTests namespace

Test Plan: phpunit with and without Docker access

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2588