feat(backend): add Prometheus monitoring and metrics

[AtilaU19]

Description

This PR introduces Prometheus monitoring to the feedback backend to improve observability.

It adds a new /metrics endpoint (exposed on port ${METRICS_PORT}, defaulting to 3099 as per server.js) that exposes key application metrics for scraping.

Changes Made

• Added prom-client as a new backend dependency.
• Created PrometheusScrapeAgent and HTTPServer to handle metrics collection and exposure.
• Modified server.js to initialize the agent and register new metrics.
• Instrumented the application to track:
  • API call counts and errors (feedback_app_api_calls_total)
  • Webhook event counts and errors (feedback_app_webhook_events_total)
  • Feedback submission counts and failures (feedback_app_registrations_total, feedback_app_failures_total)
  • A histogram for submitted user ratings (feedback_app_ratings_histogram)
• Updated docker-compose.yml to expose the new metrics port and add the METRICS_PORT environment variable.

How to Test

1. Build and run the application:

   docker-compose up --build

2. In a separate terminal, access the new metrics endpoint:

   curl http://localhost:3099/metrics

3. You should see the default Node.js metrics and the newly defined feedback_app_ metrics.
4. Trigger a feedback submission by running through the feedback flow in a meeting.
5. Run the curl command again and verify that the feedback_app_registrations_total counter and the feedback_app_ratings_histogram_count have incremented.