Remove possible false positive detection from nginx

[Tbaile]

The nginx fork provided in NethSecurity is not the most up to date, however it doesn't suffer from all the CVEs our customers provide. This is due to systems incorrectly flagging some versions only based off the server tokens. Additionally, some tools detect issues when some headers are not applied by default, this is wrong and need to be improved due to the fact that automatic tools should ring only when an actual vulnerability is found.
The planned solution is to document how to hide such banners.

• fix(reverse proxy): removed server tokens, added good default headers #1470
• fix(reverse_proxy): disable nginx server tokens python3-nethsec#109
• feat: added nginx removal of server_tokens nethsecurity-docs#221

[Tbaile]

QA: Using dev image

1. Ui tokens
   • check that server tokens are enabled by default: uci get ns-ui.config.server_tokens
   • running the curl to the firewall's UI: curl -v -k https://127.0.0.1:9090 2>&1 >/dev/null | grep "Server:" you can see the nginx version displayed
   • now follow the docs here to disable the tokens in the ui: https://nethsecurity-docs--221.org.readthedocs.build/en/221/remote_access.html#hide-web-server-version
   • check again both the uci command and the curl to be sure the version is hidden
2. Reverse proxy
   • have a reverse proxy in the firewall
   • by using the curl, check that the reverse proxy has the server populated with the nginx version (careful, if the server proxied uses the same header, it will be overwritten)
   • apply, following the docs, the remediation: https://nethsecurity-docs--221.org.readthedocs.build/en/221/reverse_proxy.html#hide-web-server-version
   • check that the version is not present anymore