fix: set a specific user-agent (gitlab-butler/VERSION)

import argparse

import os

from importlib.metadata import version

from logging import Logger

from gitlab import (

            private_token=args.token,

            ssl_verify=not args.insecure,

            per_page=100,

            user_agent=f"gitlab-butler/{version('gitlab-butler')}",

        ),

        args.group_path,

        args.exclude,