Swap SVG on onboarding popover

Context

Users who see the more prominent button call to action for the chat are shown an onboarding popover.

There is an illustration on this popover which was a custom SVG.

Scope of this issue

At the time of implementation, that illustration was not part of GitLab SVGs. It is now available and it has also been polished. This issue is to swap the SVG of the illustration to the one from GitLab SVGs.