Add docs on how to use Nginx as a HTTPS proxy (#2735)

Co-authored-by: José Valim <jose.valim@dashbit.co>

docs/deployment/nginx_https.md

@@ -0,0 +1,45 @@
+# Nginx over HTTPS
+
+This guide shows you how to use Nginx to serve Livebook over HTTPS.
+
+## Prerequisites
+
+- Nginx installed
+- Livebook installed
+- Both Livebook and Nginx running on the same machine or within the same network
+- SSL certificate and key files
+
+## Nginx configuration
+
+Use the following Nginx config file as a starting point:
+
+```nginx
+http {
+    server {
+        listen 443 ssl;
+        server_name your_domain;  # e.g., livebook.example.com
+
+        ssl_certificate /path/to/your/ssl_certificate.crt;  # e.g., /etc/nginx/ssl/livebook.crt
+        ssl_certificate_key /path/to/your/ssl_certificate.key;  # e.g., /etc/nginx/ssl/livebook.key
+
+        location / {
+            proxy_pass http://livebook_ip:livebook_port;  # e.g., http://172.20.0.3:8080 (Livebook's default port is 8080)
+            proxy_http_version 1.1;
+            proxy_set_header Upgrade $http_upgrade;
+            proxy_set_header Connection "upgrade";
+            proxy_set_header Host $host;
+            proxy_set_header X-Real-IP $remote_addr;
+            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+            proxy_set_header X-Forwarded-Proto $scheme;
+        }
+    }
+
+    server {
+        listen 80;
+        server_name your_domain;  # e.g., livebook.example.com
+        return 301 https://$host$request_uri;
+    }
+}
+
+events {}
+```

mix.exs

@@ -248,6 +248,7 @@ defmodule Livebook.MixProject do
       "docs/deployment/docker.md",
       "docs/deployment/clustering.md",
       "docs/deployment/fips.md",
+      "docs/deployment/nginx_https.md",
       "docs/teams/intro_to_teams.md",
       "docs/teams/shared_secrets.md",
       "docs/teams/shared_file_storages.md",