Add GitHub Copilot instructions for bnd repository

[Copilot]

This PR adds comprehensive GitHub Copilot instructions to help AI-assisted development in the bnd/bndtools repository, following the best practices documented at https://gh.io/copilot-coding-agent-tips.

What's Added

Created .github/copilot-instructions.md with repository-specific guidance covering:

Build & Development Environment

• Build system requirements (Java 17, Gradle/Maven wrappers)
• Complete build commands for workspace projects, Gradle plugins, and Maven plugins
• Testing commands including running specific test classes and methods

Code Organization & Standards

• Project structure overview (bndlib, plugins, Eclipse components)
• Module naming conventions (biz.aQute.* and bndtools.* patterns)
• Testing best practices using soft assertions and temporary directory annotations
• Java coding conventions and commit message format

OSGi & API Compatibility

• Backward compatibility guidelines
• Semantic versioning requirements
• Baselining tool usage

Eclipse Plugin Development

• Instructions for launching Bndtools from Eclipse
• Guidelines for adding error/warning markers
• ExtensionFacade usage patterns

Contribution Workflow

• Git triangular workflow setup
• Pull request guidelines
• Testing requirements

Quick Reference

• Common development commands
• Key documentation files
• Resource links

Why This Helps

This file provides context-aware guidance for GitHub Copilot and other AI coding assistants, enabling them to:

• Generate code that follows bnd's specific patterns and conventions
• Suggest appropriate build and test commands
• Understand the repository structure and module organization
• Apply correct testing patterns (soft assertions, temporary directories)
• Maintain backward compatibility and API standards
• Follow the contribution workflow properly

The instructions are tailored specifically to the bnd project's unique characteristics as an OSGi development toolkit with multiple build systems, Eclipse integration, and strict compatibility requirements.

Resolves the issue to configure instructions for this repository as documented in the best practices guide.

Original prompt

Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.

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