Fix & update Dockerfile

[tueda]

Currently, running ./run.sh in the Docker container gives

root@5b6450daa211:/polybench# ./run.sh
Traceback (most recent call last):
  File "/usr/lib/python3.8/runpy.py", line 185, in _run_module_as_main
    mod_name, mod_spec, code = _get_module_details(mod_name, _Error)
  File "/usr/lib/python3.8/runpy.py", line 144, in _get_module_details
    return _get_module_details(pkg_main_name, error)
  File "/usr/lib/python3.8/runpy.py", line 111, in _get_module_details
    __import__(pkg_name)
  File "/polybench/polybench/__init__.py", line 3, in <module>
    from .version import __version__
  File "/polybench/polybench/version.py", line 6, in <module>
    import importlib_metadata
ModuleNotFoundError: No module named 'importlib_metadata'

Note that simply installing python3-importlib-metadata using apt-get does not fix the issue; when installing Poetry, an incompatibility error with zipp occurs.