Expose advanced metrics

[somaritane]

This issue is a spin off from #47

Implement relevant metrics that provide insight into:

• Edge DNS integrations
• Split brain scenarios / heartbeat
• Failover scenarios
• Reconciliation
• Load balancing strategies used

#97 can be used as reference implementation

[kuritka]

ℹ️ note : Consider implementing against the IMetrics interface.
e.g.

type IMetrics interface {
   Register() error
   Unregister() error
   UpdateIngressHostsPerStatusMetric(gslb *k8gbv1beta1.Gslb, serviceHealth map[string]string)
   UpdateHealthyRecordsMetric(gslb *k8gbv1beta1.Gslb, healthyRecords map[string][]string)

   ConcreteMetricA() (data, err)
   ConcreteMetricB() (data, err)
   ConcreteMetricC() (data, err)
...
}