Refactor Docker setup and add mock data support

- Updated .dockerignore and .gitignore for better file management.
- Introduced .env.example for environment variable configuration.
- Added docker-compose.dev.yml for development with mock data and live reload.
- Enhanced Dockerfile to include necessary dependencies and entrypoint script.
- Created mock_data.py to provide sample data for testing without OpenStack/Prometheus.
- Added unit tests for template filters in dashboard.
- Cleaned up various files for consistency and improved readability.

.env.example

@@ -0,0 +1,9 @@
+# Optional: copy to .env and set for your environment.
+# For docker-compose, add to docker-compose.yml: env_file: [.env]
+
+# PYTHONUNBUFFERED=1
+# USE_MOCK_DATA=false
+# PROMETHEUS_URL=http://127.0.0.1:1234/
+# OPENSTACK_CLOUD=distlab
+# OPENSTACK_REGION_NAME=cl2k1distlab
+# SECRET_KEY=your-secret-key