Auto-configure Git identity in WSL distros from Windows host

[klemenza]

Summary

Automatically configures Git identity (user.name and user.email) inside WSL distros by reading the values from the Windows host's Git config during bootstrap.

Problem

When developers first use Git inside a newly created WSL distro, they encounter this message:

*** Please tell me who you are.
Run
  git config --global user.email "you@example.com"
  git config --global user.name "Your Name"

This requires manual configuration even though the developer already has Git configured on their Windows host.

Solution

• Read git config --global user.name and user.email from Windows during bootstrap
• Inject these values into the WSL setup script using placeholders (similar to WIN_USERNAME_PLACEHOLDER)
• Automatically run git config --global commands for the admin user inside the distro
• Display configuration status in console output

Changes

• Added Git config reading from Windows host via exec.Command("git", "config", ...)
• Added Git configuration commands to bootstrap script
• Added placeholder replacement for GIT_USER_NAME_PLACEHOLDER and GIT_USER_EMAIL_PLACEHOLDER

Testing

Verify Git is configured in WSL

wsl -d trellis-<site> -- git config --global user.name
wsl -d trellis-<site> -- git config --global user.email