Add Invoice Download Feature

[ajaybor0]

As a user, I want to be able to download my invoices so that I can keep records offline.

Backend Tasks:

1. Create a new API endpoint that handles the request for downloading invoices.
2. Generate the invoice data in the appropriate format (e.g., PDF) on the server.
3. Implement proper authentication and authorization to ensure that only authorized users can download invoices.
   #Three popular HTML to PDF libraries: Puppeteer, jsPDF, and PDFKit.

Frontend Tasks:

1. Implement a "Download Invoice" button/link on the frontend, preferably on the order details page.
2. Connect the frontend to the new backend API endpoint for downloading invoices.
3. Provide user feedback, such as loading indicators or success messages, to inform users about the download status.