Cover photo should show caption by default if added to post

[dlh01]

Description of the bug

Most themes use the first photo in the article body as the cover photo, but by default, they won't display the caption from the editor. To have a cover photo with a caption, the user has to add it into the sidebar menu in the editor, which requires extra work from the publisher.

Steps To Reproduce

On a new installation of the plugin with one of the bundled themes, publish a post that contains an inline image with a caption. Download the Apple News JSON for the post, and observe that while the inline image has been promoted to the cover image, the caption isn't included.

Additional Information

No response