feat: add issue management functionalities for github

[sirkitree]

Description

• Implemented three new GitHub API integration functions:
  • list_issues: Fetches and filters repository issues with pagination support
  • update_issue: Modifies existing issues (title, body, state, labels, etc.)
  • add_issue_comment: Adds comments to existing issues
• Added corresponding TypeScript interfaces and input validation
• Integrated error handling for API rate limits and permission issues
• Added unit tests for new functionality

Server Details

• Server: github
• Changes to: Core functionality, API integration, testing suite

Motivation and Context

These additions complete the core issue management functionality of the GitHub MCP Server, allowing LLMs to fully interact with GitHub's issue system. This enables automated issue tracking, updates, and communication through the MCP protocol.

How Has This Been Tested?

• Unit tests covering success and error cases for all new functions
• Integration tests with actual GitHub API
• Tested pagination handling with large issue sets
• Verified proper error handling for:
  • Invalid issue numbers
  • Missing permissions
  • Rate limiting
  • Malformed input data

Breaking Changes

No breaking changes - new functionality only

Types of changes

• [ ] New MCP Server
• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation update

Checklist

• [x] I have read the MCP Protocol Documentation
• [x] My server follows MCP security best practices
• [x] I have updated the server's README accordingly
• [x] I have tested this with an LLM client
• [x] My code follows the repository's style guidelines
• [x] New and existing tests pass locally
• [x] I have added appropriate error handling
• [x] I have documented all environment variables and configuration options

Additional context

The implementation uses GitHub's REST API v3 and includes proper rate limit handling and pagination support. Error messages are designed to be clear and actionable for both LLMs and human users.