Update blog post default state

[Oliviammarcello]

User Story: As a merchant installing a new theme to use for my online store, I should be able to see an accurate representation of what my theme will look like with or without placeholder content. What I see by default, should reflect what I'll see when I upload a real image

Ultimate Goal: Achieve a 1:1 experience between placeholders images and real images

More context: With the introduction of new placeholder content, and fresh eyes on the topic, we noticed some inconsistencies between the empty and populated states with images.

Video here
Notes here

Identified Problem:

1. The empty state of the blog does not accurately reflect the default styles & preset settings of the section

Expected behaviour

The default styles of blog cards placeholder images should appear with the same styles as a if they were populated with real blog images.

Task

• Match the placeholder image styles to the same default styles that would appear if image was populated
• Display a placeholder state that matches the same default presets available in the section
• Disconnect "news" preset. The blog should be empty by default