[React]: Add super simple usage of the new web worker-based cody chat

[vovakulikov]

Part of #62448
For more details and to dive deep into worker and shims problems see this sourcegraph/cody#4227

Steps to make this work

• Open Cody repository on the vk/integrate-cody-web-chat-2 branch
• At the root of the repo, run pnpm install to make sure you're up to date with all of the dependencies.
• Go to the web package (cd web)
• Build it with pnpm build
• Create a global link with pnpm link --global (Ignore the warning message about no binary)
• Open sourcegraph/sourcegraph repository on this PR branch
• Make sure you are in the root of the repo.
• Run pnpm link --global @sourcegraph/cody-web
• Run sg start web-standalone to bundle the web app and launch an instance that uses S2 for the backend. You'll need to create a login on S2 that is not federated by GitHub.
• Turn on newCodyWeb: true in your experimentalFeatures
• Have fun experimenting!

At the moment, props are hardcoded, shims are static, styles in cody web and sourcegraph web are disconnected

Test plan

• Check that old version of Cody has got no regressions