Bug: Unable to set SERVER_BASE_URL for ws connections due to a previous removal of variable prefix

[Dilrevx]

This PR(#240 ) removes the NEXT_PUBLIC_ prefix for NEXT_PUBLIC_SERVER_BASE_URL, making such variable invisible for frontend TS codes.

As a result, ws connections always fallback to the default 127.0.0.1:8001 address.

Reproduce setting

Set SERVER_BASE_URL to anything but localhost:8001.

Then all ws connections would still go for localhost:8001, while http connections are forwarded to SERVER_BASE_URL as expected.

[Dilrevx]

I wonder if you can forward ws connections via Next as well.

[Dilrevx]

Yet another feature I wish to have is to set up two dintinct environments NEXT_SERVER_BASE, and BROWSER_SERVER_BASE.

Because in my environment, next.js cannot reach python api server's public IP(i.e. 8.8.8.8.), and must go for localhost:8001; while browser api requests must go for public IP