Resolve "Multi-file editor commit panel empty state"

What does this MR do?

• Open Empty Panel by default
• Make the whole right bar clickable
• Add No Changes Illustration to panel
• Add Just Commited Illustration to panel

Why was this MR needed?

For better UX in our empty state.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• 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
• Internationalization required/considered

What are the relevant issue numbers?

Closes #4573 (closed)