feat: Implement invoice generation and emailing functionality

- Added invoice generation logic using DomPDF.
- Integrated invoice data retrieval from the API.
- Implemented language determination for invoices based on customer data.
- Added options to email invoices to customers and admin.
- Included HTML output option for direct viewing in the browser.
- Ensured proper redirection and error handling throughout the process.

api/v2/get/invoice.php

@@ -51,7 +51,7 @@ elseif (isset($criterias['list']) && $criterias['list'] =='invoice'){
     //SQL for Paging 
     $sql = 'SELECT tx.*, txi.item_id as item_id,txi.item_price as item_price, txi.item_quantity as item_quantity, txi.item_options as item_options, p.productcode, p.productname, inv.id as invoice, inv.created as invoice_created, i.language as user_language 
             FROM transactions tx 
-            left join invoice inv ON tx.id = inv.txn_id
+            left join invoice inv ON tx.txn_id = inv.txn_id
             left join transactions_items txi ON tx.id = txi.txn_id
             left join products p ON p.rowID = txi.item_id 
             left join identity i ON i.userkey = tx.account_id '.$whereclause;