fix(nginx-system): Adjust proxy buffer size

This patch fixes the nginx error messages:

```
Nginx upstream sent too big header while reading response header from upstream
```

Taking some numbers from nixCraft:

https://www.cyberciti.biz/faq/nginx-upstream-sent-too-big-header-while-reading-response-header-from-upstream/

infrastructure/nginx-system/release.yaml

@@ -87,6 +87,8 @@ spec:
         hsts-max-age: "63072000"
         enable-brotli: "true"
         use-http2: "true"
+        proxy-buffers-size: 512k
+        proxy-buffers-number: 8
 
       ## Allows customization of the tcp-services-configmap
       ##