Upgrade `realtime-react-ui` to Polaris v9

[aaronccasanova]

realtime-react-ui/package.json

Upgrade steps:

• Determine if the library|app is dependent on any of the v9 breaking changes
  (e.g. Using the ThemeProvider, using deprecated component props, etc.)

If the library|app is NOT dependent on v9 breaking changes:

• Simply update the peerDependencies section of the library|app's package.json to:
  "@shopify/polaris": "^8.0.0 || ^9.0.0"

If the library|app IS dependent on v9 breaking changes:

• Initialize the library|app
• yarn add @shopify/polaris@9.0.0-rc.2
• Update the library|app with the v9 breaking changes
• Run a type-check, build, and resolve any errors
  Once you've successfully completed a build:
• Initialize the Web Polaris v9 upgrade branch
• yarn link or yalc your library|apps build with the Web Polaris v9 upgrade branch
• Tophat the upgrade in web