JetBrains: Add standalone server
Created by: philipp-spiess
This PR adds the standalone server component that we built as a prototype for the JetBrains extension work. It's a simple html version of the Sourcegraph for JetBrains window and allows us to test the JavaScript artifacts without having to start JetBrains.
This is especially useful as it allows faster development since we don't have to rebuild & restart the JetBrains instance every time to make a change. I expect this to get more complex though as we start and introduce more bridge API methods but for now this is useful for developing the next React parts in isolation.
Test plan
yarn standalone
open localhost:3000
App preview:
Check out the client app preview documentation to learn more.