Use PHP Attribute syntax instead of Annotations + Fix some configurations

Problem/Motivation

There are a few areas in the module that need modernization and configuration fixes to align with current Drupal standards and best practices:

• Plugin Discovery: The DynamicSubscriptions plugin currently uses Doctrine annotations instead of native PHP 8 attributes.
• Missing schema configuration: The subscription_plan_id property is missing from the module's configuration schema.
• Missing logger channel: The module lacks a dedicated logger channel service to properly categorize and track its log events.

Proposed resolution

• Update the minimum core requirement to ^10.2 to safely support PHP 8 attributes.
• Refactor DynamicSubscriptions.php to use the PHP attribute syntax.
• Add the subscription_plan_id property to commerce_paypal_dynamic_subscriptions.schema.yml.
• Define the logger.channel.commerce_paypal_dynamic_subscriptions service.