Expose metrics and tracing

[donovanmuller]

Implement relevant metrics that provide insight into:

• Edge DNS integrations
• Split brain scenarios / heartbeat
• Reconciliation
• Load balancing strategies
• etc.

Metrics should be expressed as Prometheus text exposition format.

Consider the following CoreDNS plugins as reference:

• https://coredns.io/plugins/metrics/
• https://coredns.io/plugins/trace/

[somaritane]

#97 addresses generation of initial scope of prometheus metrics for the project.
Metrics are exposed at prometheus endpoints, and can scraped with 3rd party tools, as well as Prometheus Operator.
Since the scope of this issue is really wide, I suggest to chop it to smaller pieces (additional metrics, tracing support) and resolve the original, considering #97 is merged.