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

[github-actions]

This pr has been marked 'stale' due to lack of recent activity. If there is no further activity, the issue will be closed in another 30 days. Thank you for your contribution!

Please read this blog post to see the reasons why I mark issues as stale.

[rlenferink]

@geerlingguy do you see any possibility to review this change?