Preview uploaded images in the SSE

What does this MR do?

This MR adds the ability to preview uploaded images in the SSE end removes the sse_image_uploads feature flag.

This is the final iteration towards delivering #218529 (closed)

Preview

TODO

• Ensure that a temporary data URL is used to display inserted images in the WYSIWYG editor
• Ensure that the relative URL is used for images in the Markdown editor
• Update documentation screenshot
• Remove the sse_image_uploads feature flag
• UX reviewer to review the entire workflow
• Code review