Prometheus Alerting onboarding Quick-Start Guide / Recipe [documentation]

[jo-carter]

Add documentation and sample configurations for Prometheus Alerts with NGINX Ingress Controller metrics output.

This should include alerts rule configuration for common scenarios; such as for detection of outages, traffic latency spikes, http error response codes spikes, expiring certificates, and any other undesirable states of NGINX Ingress Controller that can be detected from the metrics available.

This would be the Prometheus Alerts counterpart to the sample Grafana Dashboard configuration and setup README that we currently provide.

[pdabelf5]

Thank you @jo-carter for starting this discussion. Can you please clarify on what alerts you may be looking for from the nginx /stub api and/or the plus api?