Add command line scripts / entry points via pip installation

[aaronkho]

TORAX offers a number of utility scripts to improve user interaction. However, the current recommended method of executing them is via python3 <path_to_script_in_torax_repo>. It would be easier to work with TORAX if these were converted to simple terminal commands upon pip installation of TORAX, which I understand is possible via the pyproject.toml and setuptools.

For example:
python3 <path_to_torax_repo_top>/torax/plotting/plotruns.py --outfile <full_path_to_simulation_output>
could become
torax_plot --outfile <path_to_simulation_output>

Ideally, the latter can be run from anywhere in the filesystem if TORAX is installed.