kubernetes: automatically determine the cluster CIDRs for reverse lookups

[johnbelamaric]

What would you like to be added:
Currently we manually configure the cluster CIDR, since it's not available from the API. This looks like it may be changing, see:

kubernetes/kubernetes#46508
kubernetes/enhancements#2593

Why is this needed:

If we can pull the cluster CIDRs from the API, then we can figure out the right ranges for reverse lookups, avoiding fallthrough for the reverse ranges and also avoiding manual reconfiguration when the cluster CIDRs change.

[chrisohaver]

We'd need the Cluster CIDR (for Pod IP range) and also the Service CIDR (for Service IP range).
kubernetes/enhancements#2593 seems to be leaning toward only addressing Cluster CIDR.

I've read through both kubernetes/kubernetes#46508 and kubernetes/enhancements#2593, it's unclear to me if/how these CIDRs are already available in the API. One 3 year old comment says yes (although I can't figure out if/where those APIs are exposed), most others say no. kubernetes/enhancements#2593 implies strongly they are already available (e.g. with reference to Service CIDR being available in "the Service API").

[chrisohaver]

Keeping tabs on this - I don't see any movement on the KEP (No open PR to implement it yet that I can find).