Simplify and unify PROTOCOL/DOMAIN/etc

[mscherer]

Feature Description

On #17771, @zeripath proposed to replace the current configuration (HTTP_ADDR + HTTP_PORT + maybe others) by a unified config ADDRESS.

But before coding, we need to agree on what it would look like and what would need to be achieved by the change.

Screenshots

No response

[wxiaoguang]

Too many users do wrong to their setting values. Wrong ROOT_URL, wrong LOCAL_ROOT_URL, wrong CORS/COOKIE/DOMAIN, I agree these settings should be improved.