perf(nginx): increase client body buffer size to 256k for Sentinel payloads

Increases client_body_buffer_size from default (8k-16k) to 256k to handle
Sentinel monitoring data in memory instead of buffering to disk. This eliminates
the "client request body is buffered to a temporary file" warning and improves
performance for servers with many containers (50-100+) sending health check data.

Affects both production and development nginx configurations.

docker/development/etc/nginx/site-opts.d/http.conf

@@ -13,6 +13,9 @@ charset utf-8;
 # Set max upload to 2048M
 client_max_body_size 2048M;
 
+# Set client body buffer to handle Sentinel payloads in memory
+client_body_buffer_size 256k;
+
 # Healthchecks: Set /healthcheck to be the healthcheck URL
 location /healthcheck {
     access_log off;

docker/production/etc/nginx/site-opts.d/http.conf

@@ -13,6 +13,9 @@ charset utf-8;
 # Set max upload to 2048M
 client_max_body_size 2048M;
 
+# Set client body buffer to handle Sentinel payloads in memory
+client_body_buffer_size 256k;
+
 # Healthchecks: Set /healthcheck to be the healthcheck URL
 location /healthcheck {
     access_log off;