deprecate prefect tasks

[ryanSoley]

What

deprecates the rubicon_ml.workflow module, only containing prefect tasks. rubicon-ml can still be used within custom prefect tasks as it normally would be

• these tasks have not been updated in over 3 years and are minimally leveraged by users
• they can be simply recreated, as shown in the updated example notebook that will remain in the docs
• frequent major updates to prefect have caused conflicts and vulnerabilities we no longer want to deal with inside rubicon-ml by having prefect as a dependency

How to Test

• python -m pytest

[ryanSoley]

after this is merged and released, a followup will remove the tasks.py file and the prefect dependency from the setup, requirements, and environments