openforms: opt in rate limit /discovery endpoint

[sjoerdie]

 default.conf: |
    # Rate limiting configuration - allow 1 request per second. 10m can track about 80000 clients.
    limit_req_zone $binary_remote_addr zone={{ include "openforms.fullname" . }}.{{ .Release.Namespace }}_discover:10m rate=1r/s;

Make it opt in, you might want to configure this at the infrastructure level (ingress / loadbalancer / etc).

[Tiho0135]

https://nginx.org/en/docs/http/ngx_http_limit_req_module.html

[Tiho0135]

https://github.com/maykinmedia/charts/blob/main/charts/openforms/templates/configmap-nginx.yaml#L26

[Tiho0135]

k8s Nginx ingress doc:

https://github.com/kubernetes/ingress-nginx/blob/main/docs/user-guide/nginx-configuration/annotations.md#rate-limiting

[Tiho0135]

I think it is indeed better that this rate limit can be configured at ingress nginx level, rather than as it is done in the nginx configmap.
In addition we can consider which of the other options we might need or good to implement .