feat: add discount functionality to sales and purchase transactions

- Introduced discount_type and discount fields in Bills and SalesReceipts controllers.
- Updated database migrations to include discount and discount_type in estimates and credit notes tables.
- Enhanced SaleReceipt and SaleEstimate models to support discount attributes.
- Implemented formatting for discount amounts in transformers and PDF templates.
- Updated email templates to display discount information.

This commit enhances the handling of discounts across various transaction types, improving the overall functionality and user experience.

packages/server/src/database/migrations/20241128081259_add_discount_to_estimates_table.js

@@ -4,7 +4,7 @@
  */
 exports.up = function(knex) {
   return knex.schema.alterTable('sales_estimates', (table) => {
-    table.decimal('discount', 10, 2).nullable().after('credited_amount');
+    table.decimal('discount', 10, 2).nullable().after('amount');
     table.string('discount_type').nullable().after('discount');
 
     table.decimal('adjustment', 10, 2).nullable().after('discount_type'); 

packages/server/src/database/migrations/20241128090222_add_discount_to_credit_notes_table.js

@@ -4,7 +4,7 @@
  */
 exports.up = function(knex) {
   return knex.schema.alterTable('credit_notes', (table) => {
-    table.decimal('discount', 10, 2).nullable().after('credited_amount');
+    table.decimal('discount', 10, 2).nullable().after('exchange_rate');
     table.string('discount_type').nullable().after('discount');
     table.decimal('adjustment', 10, 2).nullable().after('discount_type');
   });