Documentation: add ASAPQuery to your existing Prometheus-Grafana stack

[milindsrivastava1997]

Goal

Write a step-by-step guide for users who already have Prometheus and Grafana running and want to add ASAPQuery with minimal disruption.

Contents

The guide should cover:

1. Running the drop-in Docker Compose (issue Self-contained drop-in Docker Compose for existing Prom-Grafana stacks #245)
2. The one change to prometheus.yml (remote_write target)
3. The one change in Grafana (datasource URL → asap-query-engine)
4. How to verify ASAPQuery is serving accelerated queries (log output, metrics endpoint)
5. How to fall back to Prometheus if something goes wrong

Notes

Should live under docs/03-how-to-guides/operations/ alongside the existing manual stack guide. Written for an operator audience — assume familiarity with Prometheus/Grafana but no knowledge of ASAPQuery internals.