Prepare for the upcoming Symfony 7.4/8.0 release

This removes XML based container configuration and bumps minimum requirements, preparing for the upcoming Symfony 7.4/8.0 release.

What's Changed

• Switch from XML-based to PHP-based service configuration by @mpdude in #18
• Update test matrix, bump minimium requirements by @mpdude in #19

Full Changelog: 2.1.1...2.2.0