feat: add yearly option to billing plan DTO and fix validation issue

[AndreD17]

Pull Request

Description

This PR resolves validation issues in BillingPlanDto to ensure:
✅ Frequency only accepts "monthly" or "yearly".
✅ Amount is properly validated as a number instead of a string

• Frequency Field Validation
  • Added @IsIn(['monthly', 'yearly']) to enforce valid values.
  • Updated Swagger docs to reflect allowed values.
• Amount Field Validation
  • Changed @IsNumberString() → @IsNumber() to correctly handle numeric values.

Related Issue

Fixes: #120

Fixes #(issue)

Type of Change

✨ Feature: New functionality

• feat: New feature
• fix: Bug fix
• docs: Documentation updates
• style: Code style/formatting changes
• refactor: Code refactoring
• perf: Performance improvements
• test: Test additions/updates
• chore: Build process or tooling changes
• ci: CI configuration changes
• other:

How Has This Been Tested?

Unit test with using jest to test validations

• Unit tests
• Integration tests
• Manual tests

Test Evidence

Screenshots (if applicable)

Documentation Screenshots (if applicable)

{
"name": "Premium Yearly",
"description": "Yearly plan with full features",
"frequency": "yearly",
"amount": 1200,
"is_active": true
}

Checklist

• My code follows the project's coding style
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published
• I have included a screenshot showing all tests passing
• [] I have included documentation screenshots (if applicable)

Additional Notes

Further validation can be added if required, such as ensuring yearly pricing is 12x the monthly price.