create_app script_info argument incompatability between Flask versions

[rsyring]

  File "/home/rsyring/projects/keg-src/keg/cli.py", line 64, in get_command
    info.load_app()
  File "/home/rsyring/projects/keg-src/.tox/py39-lowest/lib/python3.9/site-packages/flask/cli.py", line 381, in load_app
    app = call_factory(self, self.create_app)
  File "/home/rsyring/projects/keg-src/.tox/py39-lowest/lib/python3.9/site-packages/flask/cli.py", line 117, in call_factory
    return app_factory(script_info)
TypeError: create_app() takes 1 positional argument but 2 were given

That's the result in Flask 1.x if our create_app() doesn't have a positional argument for script info. But in 2.0 script_info support is deprecated and in 2.1 it's removed. This issue is just tracking this disconnect and if we get to only supporting Flask 2.0 plus, then we can cleanup some code in cli.py:CLILoader.create_app().