Agent Autoconfig callback is not IPv6 ready

https://github.com/cryostatio/cryostat-operator/blob/088ffea7b12635919d26459942f583587b60b7e5/internal/webhooks/agent/pod_defaulter.go#L465

The callback hostname fallback for the Pod IP assumes an IPv4 address. It should check if the Pod IP is IPv4 or IPv6 address and handle these accordingly. The transformation for IPv6 addresses to hostnames should probably just be to enclose the address in square brackets (`[1:2:3:4]`).

Start at internal/webhooks/agent/pod_defaulter.go around line 465, where the callback hostname fallback uses the Pod IP. Check whether the address is IPv4 or IPv6 and ensure IPv6 callback hostnames use bracketed addresses; done means both address families produce valid callback hostnames.

Written by the indexing model from the issue text.