Add Temporal Cloud OpenMetrics Prometheus+Grafana demo with scenario workflows

[deepika-awasthi]

What was changed

• Added a temporalcloudopenmetrics demo that shows how to scrape Temporal Cloud OpenMetrics with Prometheus and visualize in Grafana.
• Included Docker Compose setup + Prometheus scrape config + Grafana provisioning (datasource + dashboard).
• Added a simple Java worker + starter that can run common scenarios (success/fail/cancel/continue/timeout) to generate dashboard data.

Why?

To provide an end-to-end, copy/paste friendly reference for Temporal Cloud customers who want to:

• verify OpenMetrics scraping quickly
• get a working Grafana dashboard with minimal setup
• generate real workflow/activity events to confirm metrics are flowing

Checklist

1. How was this tested:

• docker compose up -d and verified:
  • Grafana loads at http://localhost:3001 and the dashboard is present
  • Prometheus loads at http://localhost:9093 and scrape target is UP
• Ran the sample:
  • ./gradlew -q execute -PmainClass=io.temporal.samples.temporalcloudopenmetrics.WorkerMain
  • ./gradlew -q execute -PmainClass=io.temporal.samples.temporalcloudopenmetrics.Starter
  • Confirmed metrics populate in Grafana panels and queries return data in Prometheus

2. Any docs updates needed?

• README added/updated inside the demo folder with step-by-step setup instructions.