[SDTEST-3223] Use -c flag for git safe.directory instead of modifying global config

[anmarchenko]

Summary

• Replaced proactive global git config modification with per-command -c safe.directory=<path> flag
• Added getSafeDirectoryConfig() function that caches the repository root path (via sync.Once)
• Updated execGit() and execGitStringWithInput() to automatically include the safe.directory config
• Removed the code in getLocalGitData() that was adding entries to global git config

Why

The previous approach modified the global git config by running:

git config --global --add safe.directory <path>

This caused several problems:

1. Config pollution: Using --add creates duplicate entries on repeated runs
2. Security: Modifying global config affects all repositories, not just the current one
3. Persistence: Changes remain after the tool finishes running

Solution

Instead of modifying global config, we now pass safe.directory as a command-line config override:

git -c safe.directory=/path/to/repo <command>

Benefits:

• No modification to any config files (global, local, or system)
• Only affects the single command execution
• Cannot cause config pollution
• More secure (isolated to single invocation)
• Repository root is cached via sync.Once for performance

Test plan

• All existing tests pass (make test)
• Smoke testing with local git repository
• Manual testing in CI environment with different file ownership (e.g., Docker container)

[tonyredondo]

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