Add viewBox to empty-state-agents.svg

Purpose

This image is used in the empty state component, which allows setting image height as a parameter. I think we can add the viewBox property in order to fix image distortion when image height is set.

Screenshots

Before	After

Checklist

For a new icon and/or illustration:

• [-] 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.