feat: Introduce iperf3 Kubernetes network monitor

Add core components for continuous cluster network validation:
- Python exporter (`exporter/`) to run iperf3 tests and expose Prometheus metrics.
- Helm chart (`charts/iperf3-monitor/`) for deploying the exporter as a
  Deployment and iperf3 server as a DaemonSet.
- CI/CD workflow (`.github/workflows/release.yml`) for building/publishing
  images and charts on tag creation.
- Initial documentation, license, and `.gitignore`.

exporter/Dockerfile

@@ -0,0 +1,34 @@
+# Stage 1: Build stage with dependencies
+FROM python:3.9-slim as builder
+
+WORKDIR /app
+
+# Install iperf3 and build dependencies
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends gcc iperf3 libiperf-dev && \
+    rm -rf /var/lib/apt/lists/*
+
+# Install Python dependencies
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Stage 2: Final runtime stage
+FROM python:3.9-slim
+
+WORKDIR /app
+
+# Copy iperf3 binary and library from the builder stage
+COPY --from=builder /usr/bin/iperf3 /usr/bin/iperf3
+COPY --from=builder /usr/lib/x86_64-linux-gnu/libiperf.so.0 /usr/lib/x86_64-linux-gnu/libiperf.so.0
+
+# Copy installed Python packages from the builder stage
+COPY --from=builder /usr/local/lib/python3.9/site-packages /usr/local/lib/python3.9/site-packages
+
+# Copy the exporter application code
+COPY exporter.py .
+
+# Expose the metrics port
+EXPOSE 9876
+
+# Set the entrypoint
+CMD ["python", "exporter.py"]