Add `resolver` to crowdsec_nginx.conf

[Fijxu]

When the bouncer tries to validate the captcha with the captcha service selected by the user it fails with [lua] crowdsec.lua:689: Allow(): Error while validating captcha: no resolver defined to resolve "example.com" in the error logs of NGINX/Openresty without sending the request to the captcha service making the captcha useless because the form can be filled with anything and It will pass.

The https://docs.crowdsec.net/u/bouncers/nginx/#nginx-configuration pages shows resolver 8.8.8.8 ipv6=off; and when I added that to the configuration, the bouncer was able to verify key with the captcha backend selected.

Feel free to change the resolver used.

[blotus]

Hello,

We did not add the resolver directive in the default configuration because it can break some nginx configuration:

• If you have already set it in the global nginx configuration, nginx will refuse to start due to the duplicated directive
• There's no guarantee that traffic to the resolver we choose will be allowed, which will lead to runtime errors
• It's hard to chose a default value: some people will not want to send their DNS queries to Cloudflare, Google or any other 4rd party

Because of this, and because you need to modify the configuration to enable captcha support anyway, it's better to leave it to the user to set it up if required.