feat(nvidia_jetson): Add initial publish.py script for NVIDIA Jetson

This commit introduces the core `publish.py` script, enabling primary video capture and streaming capabilities for NVIDIA Jetson devices.

The script provides the foundational logic for Raspberry Ninja on the Jetson platform, including:
- GStreamer pipeline management for video capture, processing, and hardware-accelerated encoding.
- Support for RTMP and WebRTC (VDO.Ninja) video publishing.
- Robust signal handling for graceful application shutdown and cleanup.
- Integration points for platform-specific optimizations and system services.

This is a crucial component for transforming Jetson boards into wireless HDMI video capture devices.

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Author: steveseguin