[git] feat: load user name and email

[xiangma9712]

Description

Add two optional env variable GIT_USER_NAME and GIT_USER_EMAIL to set git config

Server Details

• Server: git
• Changes to: tools

Motivation and Context

Default commit user is not specific and not suitable for team development

How Has This Been Tested?

This change it self is committed by MCP with inspector

Breaking Changes

No: it's optional and nothing happens to existing users

Types of changes

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

Checklist

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

Additional context