Add POI Monitor Service: Real-time POI Discrepancy Notification System

[MoonBoi9001]

This PR introduces a new service to the graphix project that notifies about discrepancies/reuse in Proof of Indexing (POI) submissions that indexers submit across The Graph network.

New Service Overview

The POI Monitor/Notification service:

• Detects when indexers submit different POIs for the same deployment/block
• Identifies POI reuse across different deployments/blocks
• Sends notifications to Slack when discrepancies are found (via webhook)
• Prevents duplicate notifications through POI set tracking

Integration with Existing Services

• Uses the existing GraphQL API exposed by the Rust service
• Queries indexers and poiAgreementRatios endpoints
• No changes required to the Rust service or its configuration
• Runs as a separate container alongside the main service

New Files and Structure

services/poi_monitor/
├── Dockerfile                  # Container configuration
├── README.md                   # Service documentation
├── migrations/                 # Database migrations
├── src/                        # Source code
│   ├── analyzer.py             # POI analysis logic
│   ├── database.py             # Database operations
│   ├── migration.py            # Migration handling
│   ├── monitor.py              # Main service loop
│   └── notification.py         # Slack notifications
└── tests/                      # Test suite

Configuration Changes

• Added compose/dev.dependencies.yml for service configuration
• Added environment variable templates (.env.example)
• Updated .gitignore for new service patterns

Testing

• Test suite with >75% coverage
• Added GitHub workflow for automated testing
• Integration tests for database operations and POI analysis

Documentation

• Detailed README with setup instructions
• Technical implementation details
• Service limitations and behavior documentation