feat: Updated various commercetools projects settings. Made change management more robust

[demeyerthom]

Requires merging of labd/commercetools-node-mock#333

This pull request introduces several improvements and new features to the commercetools project settings resource, focusing on enhanced configuration options and more robust change management. The main themes are expanded support for carts and shopping lists configuration, improved documentation, and the addition of business unit search indexing. It also removes some internal utility code that is no longer needed.

Expanded configuration options and change management:

• Added support for configuring shopping_lists with delete_days_after_last_modification, mirroring the carts configuration and improving lifecycle management. [1] [2] [3]
• Enhanced carts configuration with new options: price_rounding_mode and tax_rounding_mode, and made the change management logic more robust and explicit for all carts settings. [1] [2] [3] [4] [5]
• Added support for enabling search indexing for business units via enable_search_index_business_units, including corresponding update logic. [1] [2] [3]

Documentation and examples:

• Updated documentation and examples to reflect new configuration options for carts, shopping lists, and business unit search indexing. [1] [2] [3] [4] [5] [6] [7] [8]
• Added a changelog entry summarizing the update and the improvements to change management.

Codebase cleanup:

• Removed unused internal utility files: internal/custommodifiers/booldefault.go and internal/custommodifiers/emptylist.go, simplifying the codebase. [1] [2]

These changes make project settings management more flexible and robust, and ensure documentation and examples are up to date with the new features.