Updated structure for the Merchant Center documentation

We've reorganized the Merchant Center documentation to offer you a better user experience. The new navigation structure is more intuitive and follows a logical content flow that ensures improved clarity, helping you find content with ease.

Changes:

• [Doc] Added the following chapters: Customization
• [Doc] Renamed the following chapters:
  • Projects and Organizations to Accounts and administration
  • Settings to Project configuration
  • Products to Product catalog
  • Orders to Order management
  • Operations to Import
• [Doc] Moved the following pages:
  • Custom Applications, Custom Views, and Connectors to Customization
  • Organizations, Projects, Teams, and User permissions to Accounts and administration > Administration
  • Product Types and Attributes and Storefront Product Order to Product catalog
  • Dashboard to Order management