Proposed changes

Tweaks product selector schema to include an "extUrl" property. This property is then used in handling to assign target="_blank" when rendered.

Example:

- productGroup: Test External Links
  products:
      - title: "NGINX.org"
        url: https://nginx.org/index.html
        extUrl: true

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation (README.md and CHANGELOG.md)