fix: remove amount if value 0 for full refund

[Benjamin-Freoua-Alma]

Reason for change

If we send amount 0 in the payload, the refund doesn't make a full refund. To make a full refund we need to send amount: null or remove the amount key in the payload.
This PR remove the amount in the payload if the amount equal 0 to make a full refund.

Linear task

Code changes

We removed the amount in refund DTO if amount === 0 for make a full refund

How to test

As a reviewer, you are encouraged to test the PR locally.

Checklist for authors and reviewers

• The title of the PR uses business wording, not technical jargon, for the changelog readers to understand it
• The PR implements the changes asked in the referenced task / issue
• The automated tests are compliant with the testing strategy
• The tests are relevant, and cover the corner/error cases, not only the happy path
• You understand the impact of this PR on existing code/features
• The changes include adequate logging and Datadog traces
• Documentation is updated (API, developer documentation, ADR, Notion...)

Non applicable

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
2.0% Duplication on New Code

See analysis details on SonarQube Cloud