[Security] Enable Aqua scanner on PR.

Need to scan for vulnerabilities on code changes.

Add new workflow (aqua.yml) to trigger vulnerability scanner on PR. Scanner in "audit mode" for now (non blocking).

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

[ ] 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...)

alma / alma-monthlypayments-magento2