Add lazy option to UserAvatarImage

What does this MR do?

EE MR, https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3163

• Add lazy option to UserAvatarImage

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Going to be used in asynchronous participants Deliverable, https://gitlab.com/gitlab-org/gitlab-ce/issues/23206

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • 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?