feat: add optional domain field

[dni]

closes #119
closes #5

adds an optional domain field and uses it for lnurl if set, else it falls back to current host like we had.

redirect required for static urls, example nginx redirect. now you can run your lnbits on https://test.b1tco1n.org but have a lightning address on b1tco1n.org and still run something else on https://b1tco1n.org/ you could also run multiple domains on lnbits and have different domains for different links.

server {
  server_name b1tco1n.org;
  root /var/www/b1tco1n;
  index index.html;
  location ^~ /.well-known/ {
      return 301 https://test.b1tco1n.org$request_uri;
  }
  location / {
    try_files $uri $uri/ =404;
  }
    listen 443 ssl; # managed by certbot
    ssl_certificate /etc/letsencrypt/live/b1tco1n.org/fullchain.pem; # managed by certbot
    ssl_certificate_key /etc/letsencrypt/live/b1tco1n.org/privkey.pem; # managed by certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by certbot
}
server {
    if ($host = b1tco1n.org) {
        return 301 https://$host$request_uri;
    } # managed by certbot
  server_name b1tco1n.org;
    listen 80;
    return 404; # managed by certbot
}

[DoktorShift]

We MUST ship this with additional docs. Else the new "domain" field will cause upcoming confusion and errors.

Nginx config & Caddyfile config we need to provide in docs.