update http2 max size so big psbt are not problem

Production/nginx.tmpl

@@ -155,6 +155,7 @@ proxy_set_header X-Forwarded-Port $proxy_x_forwarded_port;
 proxy_buffer_size          128k;
 proxy_buffers              4 256k;
 proxy_busy_buffers_size    256k;
+http2_max_field_size       32k;
 
 # Mitigate httpoxy attack (see README for details)
 proxy_set_header Proxy "";