Add support for extra_http_parameters per vhost

[rlenferink]

This adds support for vhost HTTP parameters outside the server block (e.g. for Websocket proxying).

Example:

  - listen: "80"
    server_name: "code.loc"
    extra_http_parameters: |
      map $http_upgrade $connection_upgrade {
          default upgrade;
          ''      close;
      }
    extra_parameters: |
      location / {
          proxy_pass http://container-vm1.loc:8443/;

          proxy_set_header Host $host;
          proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
          proxy_set_header X-Forwarded-Host $host;
          proxy_set_header X-Forwarded-Proto $scheme;
          proxy_redirect off;
          proxy_http_version 1.1;

          proxy_set_header Upgrade $http_upgrade;
          proxy_set_header Connection $connection_upgrade;
      }

Xref: https://nginx.org/en/docs/http/websocket.html