Handle payment_intent.payment_failed when card is not accepted

[Nnachevvv]

When payment is initiated with payment_intent.created event and the card is not accepted by some reason in Stripe, it sends payment_intent.payment_failed event which we currently don't handle.

This results in donations staying in status waiting, however the closest correct status should be 'declined'.

This PR fixes that

Closes #548

Motivation and context

Testing

Steps to test

1. I followed the document which we have in order to setup stripe:
   https://github.com/podkrepi-bg/api/blob/master/TESTING.md

2. Executed stripe trigger:

stripe trigger payment_intent.payment_failed --override payment_intent:metadata.campaignId=a57c8d72-39e0-45e8-ab59-ea84f371a35a --override payment_intent:currency=BGN

Donations that have been declined before executing the command above:

Donations after executing the command above:

[github-actions]

✅ Tests will run for this PR. Once they succeed it can be merged.

[igoychev]

looks great, and also kudos for adding the test!