feat(active-campaigns): override is-new-contact for legacy contacts

[adekbadek]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go 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:

Legacy contacts handling for ActiveCampaign.

How to test the changes in this Pull Request:

1. Switch Newsletters to feat/all-details-for-contact branch
2. Setup a site with ActiveCampaign ESP & Reader Activation
3. Create a contact in AC manually, one which is not on the site
4. Register as this contact
5. Observe the new contact metadata is added in AC – NP_Account, registration or signup data, signup page URL

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[matticbot]

🎉 This PR is included in version 1.88.0-alpha.1 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 1.89.0-alpha.1 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 1.89.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀