Add Issue Comments functionality

[jordanpartridge]

Summary

Add comprehensive support for GitHub Issue Comments API to enable full comment management functionality.

Features to Implement

Core Comment Operations

• List comments on an issue
• Get a specific comment
• Create new comments
• Update existing comments
• Delete comments

Comment Reactions

• Add reactions to comments
• Remove reactions from comments
• List reactions on comments

GitHub API Endpoints

• GET /repos/{owner}/{repo}/issues/{issue_number}/comments
• GET /repos/{owner}/{repo}/issues/comments/{comment_id}
• POST /repos/{owner}/{repo}/issues/{issue_number}/comments
• PATCH /repos/{owner}/{repo}/issues/comments/{comment_id}
• DELETE /repos/{owner}/{repo}/issues/comments/{comment_id}

Priority

High - Comments are essential for issue management workflows