Use git local configuration instead of global when available

[josecelano]

Why are we choosing to use the git global configuration over specifying it locally to the particular git repository?

Originally posted by @da2ce7 in #40 (comment)

[josecelano]

I think we should not set the committer configuration at all. The user of the command should preset the configuration. Git will choose following the priorities (local, global, system ...). Maybe we only should allow the user to overwrite committer info with options. That means we only have to remove the default value for the option.

git_user_name: str = typer.Argument(
    default_git_user_name, envvar="NL_GIT_USER_NAME"
),
git_user_email: str = typer.Argument(
    default_git_user_email, envvar="NL_GIT_USER_EMAIL"
),
git_user_signingkey: str = typer.Argument(
    default_git_user_signingkey, envvar="NL_GIT_USER_SIGNINGKEY"
),

Maybe the default configuration was added because GitPython package (the wrapper for Git we are using) was not getting that configuration correctly.