Create ROS2 workspace instructions

[marc-hanheide]

Added comprehensive instructions for copilot for setting up and developing in a ROS2 workspace, including workspace structure, build commands, package creation, testing guidelines, and common development patterns.

[Copilot]

Pull Request Overview

This PR adds comprehensive GitHub Copilot instructions for ROS2 workspace development, providing clear guidelines and best practices for working with ROS2 in a dev container environment. The instructions establish standardized development patterns and workspace structure rules.

Key changes:

• Added detailed ROS2 workspace structure and build system guidelines
• Documented proper package creation, testing, and development workflows
• Established clear rules for Python environment management and dependency handling

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