Make integration test settings overridable per ENV

[stollr]

Description (*)

In the bootstrap.php of the integration test framework several settings are derived from the defined constants.

$settings = new \Magento\TestFramework\Bootstrap\Settings($testsBaseDir, get_defined_constants());

But this is very static and unflexible. This PR improves the situation by replacing the values of the constants by environment variables.

$settings = new \Magento\TestFramework\Bootstrap\Settings($testsBaseDir, array_replace(
    get_defined_constants(),
    getenv()
));

Fixed Issues (if relevant)

1. Fixes Allow overriding constant values of integration test settings per ENV #40525

Manual testing scenarios (*)

1. Make sure that the TESTS_CLEANUP is set to enabled in your phpunit.xml.dist
2. Run TESTS_CLEANUP=disabled vendor/bin/phpunit -c dev/tests/integration/phpunit.xml.dist

This should not trigger a re-installation of Magento in the test database.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (not applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

[m2-assistant]

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