Add whitelist-source-range (or better allowlist-source-range) annotation

[sebastian-philipp]

Hi everyone,

The nginx ingress supports a whitelist-source-range annotations, which is interesting for exposing internal services only to some source IPs: nginx.ingress.kubernetes.io/whitelist-source-range.

Would be great to have this as well. I imagine we need to somehow codify it into the generated reverse proxy configuration.

See also https://stackoverflow.com/questions/66942651/how-to-expose-internal-services-in-kuberenetes-via-ingress-controller

Researching a bit more, alternatively we could also use something like authentication, but this also is not supported here.