feat(PHP): update default PHP version to 8.3

[mrrobot47]

This pull request updates the default PHP version used in the application from 8.2 to 8.3. The changes ensure that new sites and Docker configurations will use PHP 8.3 by default, improving compatibility with the latest PHP features and security updates.

Default PHP version updates:

• Changed the default PHP version in the __construct method of src/PHP.php from latest to 8.3, clarifying the default for site creation.
• Updated the logic in the create method of src/PHP.php so that when the minimum supported version is 8, it now sets php_version to 8.3 instead of 8.2.

Docker configuration update:

• Modified the PHP Docker image selection in generate_docker_compose_yml in src/Site_PHP_Docker.php to use easyengine/php8.3 when the PHP version is set to latest.