This commit adds the Go binding for `git_commit_create_buffer`. This
will be used to support the 1.2.0 commit create callback.
(cherry picked from commit fbaf9d1d1a)
add wrapper for `git_repository_item_path`
(cherry picked from commit a4d202ed7b)
Co-authored-by: Vladimir Buzuev <44682889+vladimir-buzuev@users.noreply.github.com>