Demonstrate first-class PHP configuration (core PR #6946)

[TavoNiievez]

Changes

• Delete codeception.yml and tests/Functional.suite.yml.

• Add their PHP equivalents:

  codeception.php

  return GlobalConfig::create()
      ->namespace('App\Tests')
      ->supportNamespace('Support')
      ->paths(tests: 'tests', output: 'tests/_output', data: 'tests/Support/Data', support: 'tests/Support', envs: 'tests/_envs')
      ->actorSuffix('Tester')
      ->extension(RunFailed::class)
      ->params('.env', '.env.test')
      ->settings(shuffle: true, colors: true, reportUselessTests: true);

  tests/Functional.suite.php

  return SuiteConfig::create()
      ->actor('FunctionalTester')
      ->module('Asserts')
      ->module('Symfony', ['app_path' => 'src', 'environment' => 'test'])
      ->module('Doctrine', ['cleanup' => true], depends: 'Symfony');

• composer.json — link the core to the php_config branch (that is where the builders live):

  "repositories": [
      { "type": "vcs", "url": "https://github.com/Codeception/Codeception.git" }
  ],
  "require-dev": {
      "codeception/codeception": "dev-php_config as 5.3.x-dev"
  }

  The inline alias keeps module-doctrine (^5.1) and the module-asserts (< 5.0) constraints
  satisfied. composer.lock is refreshed and pins the branch commit so CI's composer install works.

• CI (.github/workflows/symfony.yml) — also triggers on 8.1-php-config.