feat: add Docker Compose support for local orchestration (closes #15)

[PuneethM-06]

Summary

This PR introduces Docker Compose support for the linux-sysmonitor project, making local development and orchestration simpler. The application can now be started with a single command while supporting persistent log storage, environment-based configuration, and multi-container networking.

Changes

• Added docker-compose.yml for local orchestration.
• Configured the sysmonitor service to build from the local Dockerfile.
• Added a named volume (sysmonitor_logs) to persist log files.
• Mounted the volume to /app/logs.
• Injected runtime configuration using environment variables:
  • LOG_LEVEL
  • CHECK_INTERVAL
  • TARGET_HOST
• Added a secondary webserver service using the official nginx:alpine image.
• Configured sysmonitor to communicate with the webserver service using Docker Compose's default network.
• Added depends_on to ensure the webserver starts before the monitoring service.

Validation

• Successfully started services using docker compose up --build.
• Verified named volume creation and log persistence across container recreation.
• Confirmed environment variable injection.
• Verified inter-container communication by resolving and pinging the webserver service through the default Docker Compose network.

Notes

• restart: unless-stopped has been deferred because the current health-check.sh is a one-time execution script. This will be enabled once the application is enhanced to run as a long-running monitoring service.
• Existing journalctl and CPU parsing issues are tracked separately and are outside the scope of this PR.

[PuneethM-06]

Note: Environment variables have been added to demonstrate Docker Compose configuration. The current version of health-check.sh does not yet use them; support will be added in a future enhancement.