feat: added events to subscription

[demeyerthom]

This pull request introduces several updates across multiple files to enhance the functionality of the Commercetools Terraform provider. The most significant changes include adding support for event subscriptions, updating dependencies in the go.mod file, and improving the handling of subscription update actions. Below is a breakdown of the most important changes grouped by theme:

Support for Event Subscriptions:

• Added a new event block to the subscription schema, allowing users to subscribe to specific events. This includes attributes for resource_type_id and types, with detailed descriptions provided in docs/resources/subscription.md and internal/resources/subscription/resource.go. [1] [2]
• Implemented the Event struct in internal/resources/subscription/model.go, including methods to convert between native and platform event subscription formats.
• Updated subscription creation and update logic to handle event subscriptions, including the addition of eventsAction in the OrderSubscriptionTypesActions function. [1] [2]

Dependency Updates:

• Upgraded several dependencies in the go.mod file, including golang.org/x/text, golang.org/x/crypto, and github.com/labd/commercetools-go-sdk, to ensure compatibility and leverage the latest features. [1] [2]

Subscription Update Logic Improvements:

• Refactored the OrderSubscriptionTypesActions function to include event subscriptions and ensure proper ordering of actions based on non-empty attributes.
• Updated tests in internal/resources/subscription/model_test.go to cover scenarios involving event subscriptions and validate the updated logic. [1] [2]

Documentation Enhancements:

• Added examples and descriptions for event subscriptions in docs/resources/subscription.md and examples/resources/commercetools_subscription/resource.tf, providing clear guidance for users. [1] [2]

Minor Code Improvements:

• Updated the SortOrder field in resourceCartDiscountCreate to use a helper function for string references, improving code consistency.