fix: can set installmentsCount to 24

[joyet-simon]

Reason for change

Linear task

Code changes

Instalments count can be upper that 12 and just need to be positive

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