Bump post max size to 25M

Build artifcats are limited to 10MB per piece and we have
logs/diffoscope and json can become a little over 20M.

roles/rebuilderd/templates/nginx.d.conf.j2

@@ -51,7 +51,7 @@ server {
     }
 
     location /api/v0/build/report {
-	    client_max_body_size 20M;
+	    client_max_body_size 25M;
             proxy_set_header    X-Real-IP          $remote_addr;
 	    proxy_pass http://127.0.0.1:8484;
     }