Use `dill.dumps` and `dill.loads` serialization instead of `pickle`

[GregoirePelegrin]

Summary

This is needed to allow passing more complex arguments to celery tasks (i.e. lambda expressions, instances from dynamically generated classes).
For additional information, please refer to both celery/celery#9091 (comment) and the initial StackOverflow post.

Related issue

This issue is the sister issue from celery/celery#9091 (comment).