feat: add configuration files and scripts for project setup ✨

🚀 Breaking Changes:
- Introduced new environment variables for GitLab API integration
- Added validation script for PR checks
- Updated package.json with new scripts for testing and formatting

📝 Details:
- Added .prettierrc and .eslintrc.json for code formatting and linting
- Created .env.example for environment variable setup
- Updated CHANGELOG.md with recent changes
- Added documentation for GitHub secrets setup

CHANGELOG.md

@@ -31,6 +31,7 @@
 ### Fixed
 
 - Fixed issue where GitLab users without profile pictures would cause JSON-RPC errors
+
   - Changed `avatar_url` field to be nullable in GitLabUserSchema
   - This allows proper handling of users without avatars in GitLab API responses
   - See: [PR #55](https://github.com/zereight/gitlab-mcp/pull/55)