Upgrade to Python 3.10

This PR is to test if simply bumping to Python 3.10 could work.

Files modified:

• https://github.com/codalab/codabench/blob/python3.10/Dockerfile
• https://github.com/codalab/codabench/blob/python3.10/Dockerfile.compute_worker
• https://github.com/codalab/codabench/blob/python3.10/Dockerfile.celery

Files to be modified:

• https://github.com/codalab/codabench/blob/python3.10/Dockerfile.flower
• https://github.com/codalab/codabench/blob/python3.10/Dockerfile.rabbitmq