Python compatibility cqlsh

Python compatibility for cqlsh

cqlsh requires Python 3.9. If your Linux distribution provides a newer Python version by default, you must install Python 3.9 alongside it and explicitly tell cqlsh which interpreter to use. You can do this by setting the CQLSH_PYTHON environment variable when running cqlsh: sudo -u cassandra CQLSH_PYTHON=/path/to/python3.9 cqlsh.