Support galaxy `galaxy_user` and `galaxy_group` from planemo commands

Currently when running `planemo test` against a local Galaxy 23.0 installation (dockerized, installed under root), planemo will error out with a message like:
```
Executing: galaxyctl start
Error: 1 validation error for Settings
galaxy_user
galaxy_user is required when running as root (type=value_error)
Problem running Galaxy command [].
Traceback (most recent call last):
File "/usr/local/bin/planemo", line 8, in
sys.exit(planemo())
File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1130, in __call__
return self.main(*args, **kwargs)
File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1055, in main
rv = self.invoke(ctx)
File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1657, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1404, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 760, in invoke
return __callback(*args, **kwargs)
File "/usr/local/lib/python3.8/dist-packages/click/decorators.py", line 84, in new_func
return ctx.invoke(f, obj, *args, **kwargs)
File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 760, in invoke
return __callback(*args, **kwargs)
File "/usr/local/lib/python3.8/dist-packages/planemo/cli.py", line 102, in handle_blended_options
return f(*args, **kwds)
File "/usr/local/lib/python3.8/dist-packages/planemo/commands/cmd_test.py", line 75, in cli
return_value = test_runnables(ctx, runnables, original_paths=uris, **kwds)
File "/usr/local/lib/python3.8/dist-packages/planemo/engine/test.py", line 13, in test_runnables
test_data = engine.test(runnables, test_timeout=kwds.get("test_timeout"))
File "/usr/local/lib/python3.8/dist-packages/planemo/engine/interface.py", line 76, in test
test_results = self._collect_test_results(test_cases, test_timeout)
File "/usr/local/lib/python3.8/dist-packages/planemo/engine/interface.py", line 90, in _collect_test_results
run_responses = self._run_test_cases(test_cases, test_timeout)
File "/usr/local/lib/python3.8/dist-packages/planemo/engine/galaxy.py", line 79, in _run_test_cases
with self.ensure_runnables_served(runnables) as config:
File "/usr/lib/python3.8/contextlib.py", line 113, in __enter__
return next(self.gen)
File "/usr/local/lib/python3.8/dist-packages/planemo/engine/galaxy.py", line 134, in ensure_runnables_served
with serve_daemon(self._ctx, runnables, **self._serve_kwds()) as config:
File "/usr/lib/python3.8/contextlib.py", line 113, in __enter__
return next(self.gen)
File "/usr/local/lib/python3.8/dist-packages/planemo/galaxy/serve.py", line 84, in serve_daemon
with serve(ctx, runnables, **kwds) as config:
File "/usr/lib/python3.8/contextlib.py", line 113, in __enter__
return next(self.gen)
File "/usr/local/lib/python3.8/dist-packages/planemo/galaxy/serve.py", line 22, in serve
with _serve(ctx, runnables, **kwds) as config:
File "/usr/lib/python3.8/contextlib.py", line 113, in __enter__
return next(self.gen)
File "/usr/local/lib/python3.8/dist-packages/planemo/galaxy/serve.py", line 56, in _serve
raise Exception(message)
Exception: Problem running Galaxy command [].
```

It seems like the following lines in the Galaxy config file are responsible for this: https://github.com/galaxyproject/galaxy/blob/release_23.0/lib/galaxy/config/sample/galaxy.yml.sample#L57-L63