[FEATURE] #67 Show Payment Plans in Site Health

[MaximilianoRicoTabo]

• Add payment plans if exist to each level catching pmpro_site_health_info_membership_level filter

All Submissions:

• Have you followed the Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Resolves #67 .

How to test the changes in this Pull Request:

1. Pull Site health info.
2. Observe payment plans are present for those levels with payment plans

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you successfully run tests with your changes locally?

Changelog entry

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.