feat(theme): add Theme support

[niloysikdar]

This Pull Request covers:

• Add Theme with context API
• Changes to makeStyles function to accept themeClasses inside useStyles hook
• Default Theme and types
• TSDoc comments for the Theme interface and theme props inside the Email

Resolves #88

Signed-off-by: Niloy Sikdar niloysikdar30@gmail.com

[github-actions[bot]]

🎉 This PR is included in version 1.12.0 🎉