Setup.py method is being deprecated in python package

[LaoshuBaby]

Now when you install gpxpy in python 3.11, below warning will be given:

DEPRECATION: gpxpy is being installed using the legacy 'setup.py install' method, 
because it does not have a 'pyproject.toml' and the 'wheel' package is not installed. 
pip 23.1 will enforce this behaviour change. 
A possible replacement is to enable the '--use-pep517' option. 
Discussion can be found at https://github.com/pypa/pip/issues/8559

pypa/pip#8559 provided some suggestion about this. It was also partially mentioned in #247