Introduce `create-git-pr-diff` CLI tool and enhance documentation

feat: Introduce create-git-pr-diff CLI tool and enhance documentation

• Added create-git-pr-diff CLI tool for efficient git diff generation between commits.
• Created a bash script git-diff-with-name.sh for listing changed files with their diffs.
• Provided comprehensive documentation in chat-git-diff-for-commit-msg.md for generating structured commit messages using ChatGPT.
• Included click in requirements.txt for CLI dependencies.
• Set up the package with setup.py, facilitating installation and deployment.
• Implemented the main logic in src/create_git_pr_diff_for_gpt.py, supporting detailed git diff creation and output.