Add new subgroup illustration

Purpose

For gitlab!84397 (merged)

Figma file: https://www.figma.com/file/QR0uCu8XWeRdQac1YpaVrq/267113-Seperate-group-and-project-creation?node-id=112%3A3127

Screenshots

Checklist

For a new icon and/or illustration:

• Link to related design issue: gitlab#267014 (closed)
• If this adds an icon ensure that it follows the new icon checklists.
• If this adds an illustration ensure that it follows the new illustration checklists.

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.