Enhance WebSocket load testing and remove Dependabot automation

[MovinduJay]

This pull request introduces comprehensive load and performance testing profiles for the WebSocket chat gateway, significantly expanding the coverage and flexibility of benchmarking scenarios. It also removes the existing Dependabot configuration. The most important changes are summarized below.

Testing Enhancements

• Added three new k6 load test scripts: websocket-connections.js for measuring simultaneous connection capacity, websocket-broadcast.js for Redis-to-WebSocket broadcast fanout, and websocket-fanout.js for full chat message fanout including database persistence. Each script supports environment-driven configuration for reproducibility and proper separation of throughput metrics. [1] [2] [3]
• Enhanced realtime-websocket.js to allow parameterization of target VUs, ramp and sustain durations, and added more robust acknowledgement tracking and success rate metrics. [1] [2] [3] [4] [5] [6] [7]
• Updated TESTING.md with detailed instructions and environment variable documentation for running and interpreting the new load testing profiles. This includes guidance on how to distinguish between connection capacity, broadcast fanout, and message throughput.

Dependency Management

• Removed the .github/dependabot.yml file, disabling automated dependency update PRs for all subprojects.