Integrate RazorPay Payment Gateway

**Description** :thought_balloon:
> Integrate RazorPay Payment Gateway into the application (testing mode only) and store the details of the transaction into the Firestore Database

**Guidelines** :thinking:
> - Prefetch the transaction amount from donations screen, and provide it to the RazorPay Gateway.
> - Add Wallets, UPI, Debit/Credit cards, and netbanking options
> - On completion of Transaction, show a popUp dialog displaying the result, and reroute the page to Individual_Profile_Page to show donation records
> - Store the status of the transaction into the database

**Resources** :book:
RazorPay:
> - https://razorpay.com/docs/payments/payment-gateway/flutter-integration/standard/#integration-steps
> - https://pub.dev/packages/razorpay_flutter
> - https://medium.flutterdevs.com/razorpay-payment-in-flutter-7285408d11a8

**Deadline** :hourglass:
3 days after having been assigned

Interested persons may mention their willingness to contribute here. :smiley: