Resolve "Make margin of user status emoji consistent"

What does this MR do?

Makes margin of user status emoji consistent.

Removes added whitespaces in issueables_helper.rb. Instead it adds an additional 4px margin between emoji and username via CSS.

In addition, it sets a custom font-size and line-height for the emoji.

What are the relevant issue numbers?

#49644 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Reviewed by UX

Closes #49644 (closed)