Prometheus metrics

[michaelvl]

Summary

Add Prometheus metrics to observe the health status of Gateway-API and child resources, e.g. are Crossplane child resources sync and ready.

Motivation

Metrics (and thus alerts) are essential to a health production deployment.

Proposal

[michaelvl]

This will not be implemented by the bifrost controller. Instead an example configuration of kube-state-metrics is provided in #199