Added optimized git clone script in config/rootfs/debos/scripts/git-operations.sh

[khanheric2003]

This PR implements standardized git clone optimization for KernelCI rootfs builder scripts to reduce network traffic and improve CI build performance, addressing issue #2894.

Changes Made

• Added git-operations.sh
• Created comprehensive documentation
• Added testing scripts

Technical Details

• Implements git clone --depth=1 --single-branch pattern
• Provides git_clone_optimized() function for consistent usage
• Includes error handling and branch auto-detection

[nuclearcat]

1)No existing script is refactored to call git_clone_optimized()
2)Depth hard-coded to 1 and advertised as optimisation, might break tools that need tags/history (git describe, kernel versioning, patch rebasing).
3)Repos with submodules will fail to clone / build properly
4)No SPDX header, no executable bit set, no shellcheck annotations
5)# Wrapper for backward compatibilitygit_clone() { - we dont have even such function anywhere.

The patch appears machine-generated, adds non-trivial maintenance surface, and yields no actual optimisation.
Sorry, but closing PR.