Wordpress block variation registration code for post-featured-image to include caption automatically.

custom-block-variation.js

// Define the custom block variation
wp.blocks.registerBlockVariation(
    'core/post-featured-image', // Base block type
    {
        name: 'sotp/post-featured-image', // Variation name
        title: 'Post Featured Image + Caption', // Variation title
        description: 'Displays the post\'s featured image with caption.', // Variation description
        attributes: {
            namespace: 'sotp_post_featured_image', // Custom attribute namespace
            className: 'sotp-post-featured-image' // Custom class name
        },
        scope: ['inserter'] // Block variation is available only in the inserter
    }
);