feat(deploy) : add maintenance mode with automatic toggle during deploy

deploy/nginx/sirh-docker.conf

@@ -2,6 +2,23 @@ server {
     listen 80;
     server_name sirh.malio-dev.fr;
 
+    root /var/www/sirh/public;
+
+    # Maintenance mode : si le fichier maintenance.on existe, renvoyer la page 503
+    if (-f /var/www/sirh/maintenance.on) {
+        return 503;
+    }
+
+    error_page 503 @maintenance;
+
+    location @maintenance {
+        rewrite ^(.*)$ /maintenance.html break;
+    }
+
+    location = /maintenance.html {
+        internal;
+    }
+
     location / {
         proxy_pass http://127.0.0.1:8080;
         proxy_set_header Host $host;