Add GitHub Webhooks example using HTTP source plugin

[danielgerlag]

Summary

Adds a new example demonstrating how to use the HTTP webhook source plugin to receive and process GitHub webhooks with Drasi Server.

What's included

• examples/github-webhooks/server-config.yaml — Full server configuration with:

  • HTTP webhook source with HMAC-SHA256 signature verification
  • 3 webhook route mappings (push, pull_request, issues)
  • 3 Cypher queries for filtering events
  • Log and SSE reactions for output

• examples/github-webhooks/scripts/ — Shell scripts to:

  • Start the server
  • Simulate GitHub webhook payloads (with proper HMAC signatures)
  • View query results and stream SSE events

• examples/github-webhooks/viewer/index.html — Live SSE dashboard showing webhook events in real-time

• examples/github-webhooks/README.md — Comprehensive tutorial covering:

  • Quick start with simulated webhooks
  • Connecting to a real GitHub repo using Microsoft Dev Tunnels
  • Architecture overview and extending the example

• Updated examples/README.md with the new example entry

Testing

• Config validation passes (cargo run -- validate)
• End-to-end tested: server starts, all queries run, simulated webhooks accepted (HTTP 200), query results returned correctly via API