increasd buffer size to cope with the 2022-04 SOGo update

data/mailcow_proxy.conf

@@ -18,6 +18,9 @@ server {
         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;
-        client_max_body_size 100m;
+        client_max_body_size 0;
+        proxy_buffer_size 128k;
+        proxy_buffers 64 512k;
+        proxy_busy_buffers_size 512k;
     }
 }