feat(styling): list styles

[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:

Building on #1335, adds margin to the li element, so the indentation is preserved.

Before	After

How to test the changes in this Pull Request:

1. On trunk, create a new newsletter and insert an unordered and an order list, ensure list items content is long enough to wrap to next line
2. Preview the email – observe the content wrapping does not preserve the indentation
3. Switch to this branch, observe the indentation is preserved

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?

---

• To see the specific tasks where the Asana app for GitHub is being used, see below:
  • https://app.asana.com/0/0/1208067144529568

[matticbot]

🎉 This PR is included in version 3.2.0-alpha.1 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 3.2.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀