Only show borders around markdown images in notes

What does this MR do?

Only show borders around markdown images in notes.

Still shows them around preview notes

What are the relevant issue numbers?

Fixes #55703 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides