Featured image email toggle: Explore options of matching image styles set in the theme

Currently, the Featured image displayed in the _New Post_ email template ignores the styles coming from the theme and _Post Featured Image_ block.

The goal of this task is to explore the codebase and see how easy or complicated is it to apply these styles to the Featured image in the email template.

More details and product discussion: pdtkmj-Gy-p2#comment-1170

Start by tracing the New Post email template and its Featured image, then compare that path with the theme styles and the Post Featured Image block. Review the product discussion for requirements and document whether matching those styles is feasible, including the relevant implementation options and complexity.

Written by the indexing model from the issue text.