dstack-ingress: add WebSocket proxy support

[h4x3rotab]

The kvin/dstack-ingress:wildcard image generates its nginx config via setup_nginx_conf() in the entrypoint, but the location / block is missing WebSocket upgrade headers. Without these, any WebSocket service behind dstack-ingress gets HTTP 200 instead of 101 Upgrade.

Suggested fix: add these three lines to the location / block in setup_nginx_conf():

proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";

This is safe for mixed HTTP + WebSocket traffic. $http_upgrade is empty for regular HTTP requests, and upstreams ignore Connection: upgrade when there's no valid Upgrade value. proxy_http_version 1.1 is strictly better than the default 1.0 (also enables keepalive). This is the standard nginx pattern recommended in the nginx WebSocket docs.

Current workaround: override command in docker-compose to patch the generated config before starting nginx:

command:
  - bash
  - -c
  - |
    sed -i '/proxy_pass/a\        proxy_http_version 1.1;\n        proxy_set_header Upgrade $$http_upgrade;\n        proxy_set_header Connection "upgrade";' /etc/nginx/conf.d/default.conf
    exec nginx -g "daemon off;"

[h4x3rotab]

Or maybe better to completely switch to haproxy

[h4x3rotab]

Can be fixed by #88