Symfony 8 support

[TheMilek]

Changes:

• Add ^8.0 to all Symfony package constraints
• Update minimum PHP version to ^8.2
• Update Symfony constraints from ^5.4 || ^6.4 || ^7.0 to ^6.4 || ^7.4 || ^8.0
• Migrate from XML to PHP service configuration (XmlFileLoader removed in Symfony 8)
• Update phpunit/phpunit to ^10.5 || ^11.0
• Update matthiasnoback/symfony-*-test to ^5.0 || ^6.1
• Update phpspec/phpspec to ^7.0 || ^8.0
• Update symfony/service-contracts and symfony/translation-contracts to ^3.0
• Update CI workflow to test with PHP 8.2+ and Symfony 8.0
• Simplify CI workflow by using tools: 'composer:v2, flex'