Pass Gitpod urls to the frontend

[DukeManh]

With the change from #2406, when a Gitpod workspace starts, images are built correctly but our frontend is making requests to localhost. We need to find a way to pass gitpod URLs to Next in build time.

I've tried to pass URL through build arguments but we prefer a monkey-patching approach where we don't have to touch the current configuration.

A way to do this would be generate an env.gitpod when gitpod starts with the URLs being gp URL PORT.

[humphd]

@DukeManh assigned to you.

[DukeManh]

Responsibility!

[DukeManh]

I'll continue hacking once I catch up with all the due dates coming.

[humphd]

cc'ing @raygervais and @cindyledev, who might have time and wisdom here.

[humphd]

Looks like the GitPod integration is working:

New PRs get this button attached, see #2428 for example.

Question: any issues having this here without it working fully?

[humphd]

Filed #2429 to properly document this.

[DukeManh]

Question: any issues having this here without it working fully?

We can test the frontend on it using env.staging and run npm run dev.
The doc could mention this too, like you don't have to wait for docker build if only testing the frontend.