Before, in #19732, the old home directory is not correct.
This PR introduces a new config option for git home: git.HOME_PATH,
which is default to %(APP_DATA_PATH)/home
And pass env GNUPGHOME to git command, force Gitea to use a stable GNUPGHOME directory
This module is merged from https://github.com/go-gitea/git which is a Go module to access Git through shell commands. Now it's a part of gitea's main repository for easier pull request.