Create successful/failed payment pages

[GabrielMajeri]

After the user finishes submitting his details on the EuPlătesc secure payment page, their platform will redirect them back to our app, based on the result of the transaction.

We should have two pages:

• The /payment-success page, informing the user that their payment has been successfully completed and thanking them for their cooperation.
• The /payment-failed page, informing the user that their payment failed to go through, providing them some helpful troubleshooting instructions (if possible) and asking them to retry the payment flow.