use the istio microk8s platform config

[ca-scribner]

Enhancement Proposal

Istio 1.24 introduced a microk8s platform config, available via:

istioctl install --set profile=ambient --set values.global.platform=microk8s

This appears to be able to replace our cni-bin-dir and cni-conf-dir config variables, which would nicely simplify the UX. We should investigate the changes and use this if suitable.

To be considered: should we instead expose this platform variable in our config? Probably, that way someone can use other platforms like GKE or EKS.