Centralize information about monitoring, observing, and alerting a Crossplane instance

### What's Missing?

Information around monitoring, observing, and alerting on a Crossplane instance is currently sparse and spread across different sources. We should consider publishing a section in the docs that cover this information in a central location.

This page in the ArgoCD docs is a good example of what is required: https://argo-cd.readthedocs.io/en/stable/operator-manual/metrics/

Some existing resources:
- https://github.com/crossplane/crossplane/blob/master/contributing/guide-observability.md
- https://github.com/upbound/upjet/blob/main/docs/monitoring.md
- https://docs.crossplane.io/knowledge-base/guides/troubleshoot/