Document product integration for integrating with monitoring stack (Prometheus/Grafana)

Details:

• Enabling built-in Prometheus metrics scraping
• Adding exporter for Prometheus scraping if it doesn't have built-in
• Using ServiceMonitor and/or PodMonitor in Big Bang packages
• Adding alerts to AlertManager
• Min. set of alerts that should be configured

NOTES:

• Use PodInfo as the example app in all instructions. We want someone following the documents from beginning to end able to add podinfo into Big Bang.
• Placeholders for docs will be created in this MR. Format is markdown.
• Any overlapping sections in the original package integration doc should be cleaned up with references to this doc. The original may be renamed to package-integration-supported.md.