Resolve "User profile activity feed contains broken image links"

What does this MR do?

It fixes broken lazy loading images in the activity stream due to HTML Sanitizer which had not whitelisted data-src.

Screenshots (if relevant)

Ignore the emoji ;-) the max-width is also fixed with another MR.

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #36458 (closed)