Update reverse proxy documentation

[Simon-Blandford-Onepoint]

Is your feature request related to a problem? Please describe

The documentation for reverse proxying, at least with nginx, only covers non-ssl and root without subdirectory proxying. Also, the latest requirements for being able to log into version >2.27.6 aren't included ##12690. It also shows only docker-compose examples and not single docker command line examples.

Describe the solution you'd like

Please cover more scenarios such as using Nginx SSL certificates and subdirectory proxying.

As an example, here is the nginx configuration I am using.

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    # SSL configuration
    #
    listen 443 ssl default_server;
    listen [::]:443 ssl default_server;

    ssl_certificate /etc/ssl/certs/my.domain.lan.pem;
    ssl_certificate_key /etc/ssl/private/my.domain.lan.key;

    root /var/www/html;

    index index.html index.htm index.nginx-debian.html;

    server_name _;

    location / {
        try_files $uri $uri/ =404;
    }
    location = /portainer {
        return 301 /portainer/;
    }
    location /portainer/ {
        proxy_pass https://127.0.0.1:9443/;

        proxy_set_header Host $host;
        proxy_set_header Origin "";
        proxy_set_header X-Forwarded-Proto $scheme;

        # Required for web sockets to function
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_cache_bypass $http_upgrade;
    }
}

And this is the command line I am using.

docker run -d -p 127.0.0.1:9000:9000 \
    -p 127.0.0.1:9443:9443 \
    --name portainer \
    --restart=always \
    -v /var/run/docker.sock:/var/run/docker.sock \
    -v portainer_data:/data \
    -e VIRTUAL_HOST=my.domain.lan \
    -e VIRTUAL_PORT=9443 \
    portainer/portainer-ee:lts \
    --base-url /portainer

Describe alternatives you've considered

I eventually arrived at a configuration that works for (1) logging in, (2) sub-directories, (3) SSL (re)wrapping but it took some time to get it working.

Additional context

No response