Use `upstream` directives

[Lordfirespeed]

Any hostname that we proxy_pass to should be part of an upstream block.

Example (before)

server {
    server_name whatever.durhack.com;
    proxy_pass http://127.0.0.1:8080$request_uri;
}

Example (after)

upstream whatever-backend {
    server 127.0.0.1:8080;
}

server {
    server_name whatever.durhack.com;
    proxy_pass http://whatever-backend$request_uri;
}