Fix : MPP-297 PHP 8.2 compatibility

We have an issue with PHP 8.2 with dynamic properties

Declare class properties

Test all plugins features

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

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

alma / alma-monthlypayments-magento2