feat: implement signoff feature for git commits ✍️

- Add support for signed-off-by line in commit messages with configurable option
- Refactor commit function to accept signoff parameter in git.rs
- Retrieve author name and email from repository config for signoff
- Remove redundant signoff logic from main.rs and centralize in git.rs
- Update commit call in main.rs to pass signoff requirement

Signed-off-by: mingcheng <mingcheng@apache.org>

Author: mingcheng