Expose smaller Design Management design images in GraphQL

What does this MR do?

This MR exposes smaller Design Management design images in GraphQL.

As the smaller design images are not generated immediately, and in some cases will never be generated (i.e., if the image is an SVG at time of writing), the new GraphQL field can emit null.

Issues

• #12577 (closed)
• #13815 (closed)

Related MRs

This is the third MR for #13815 (closed). These earlier two MRs may give some context to this final change.

• Generate smaller images for Designs: !22860 (merged)
• Service resized Design Management design files !25781 (merged)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done