Add price list and price list items

[JustShah]

Price List and Price List Items Management

This pull request introduces a complete Price List and Price List Items Management system within the Spree Admin. It enhances the flexibility of product pricing by associating price lists with user groups, managing price list items, and offering an improved admin interface for easier management of pricing strategies.

Key Features:

1. Add Price List Info on User Group Admin:

   • Added a column to the User Group admin interface to display and select the associated price list for each user group.
   • This feature enhances the ability to manage pricing based on specific user groups, providing a more tailored approach for different customer segments.

2. Price List Management:

   • Introduced PriceListsController to manage price lists within the admin panel.
   • Implemented form fields for the price list name, country, currency, and tax inclusion.
   • Added functionality to display price details associated with each price list.
   • Improved breadcrumb navigation for a better user experience in the admin panel.

3. Price List Items Management:

   • Introduced PriceListItemsController to manage price list items.
   • Implemented functionality to associate price list items with specific price lists and product variants.
   • Added support for entering price details, including amount, currency, and taxes.
   • Enhanced breadcrumb navigation in the admin panel for easy access to related views.

4. Model and Database Changes:

   • Introduced Spree::PriceList model to manage collections of prices associated with specific user groups and countries.
   • Added an optional association for price_list on the user_group model.
   • Created Spree::PriceListItem model to establish relationship between prices and price lists.
   • Updated Spree::Price model to include associations with price lists through price list items.
   • Added a contain_taxes attribute to the Spree::Price model to indicate whether prices include taxes.
   • Added necessary database migrations to create the spree_price_lists and spree_price_list_items tables.

Benefits:

• Flexible Pricing Strategies: Enables store owners to apply different pricing strategies based on user groups and geographical locations.
• Improved Admin Interface: Enhancements in the admin interface provide a more efficient way for administrators to manage price lists and user-specific pricing.
• Better User Group Integration: By associating price lists with user groups, administrators can offer tailored pricing to different segments of users.
• Comprehensive Price Management: With the addition of price list items and their management, administrators can now have more granular control over pricing details for products.