[SG-38607] React upgrade: Migrate to the new root API

Created by: gitstart-sourcegraph

Description

• Replace ReactDOM with new createRoot API in renderColorDebugger.tsx

Refs

SourceGraph Issue GitStart Issue

Test plan

• Make sure all CI checks passed and wait for approval from Jetbrains ext team

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.