Add options to check task definition to create an output

[hiro-o918]

What

Add a feature to create a hash of a task. The hash is created by cloudpickle.dumps to the class object of a task.

Why

Current implementation assumes that an output is determined by input parameters and requirements. But this assumption does not work, when the implementation of a task changes.

As a results, some issues can occur.

• In local development, we need to remove output .pkl to rerun tasks
  • modification_time_check can resolve this in some aspects (I like this option)
• In production with some storage (e.g. S3), backfilling or re-running can be difficult because output .pkl must be removed as well as local development.

So, adding task definition to hash resolves these issues and re-reruns tasks safely.

Discussion

• this feature depends on cloudpickle

[vaaaaanquish]

@hiro-o918 Thanks great suggestions. Is it possible to apply a yapf formatter?

[vaaaaanquish]

LGTM. I'll wait for the @Hi-king review.

[mski-iksm]

@hiro-o918 LGTM! Thank you for your contribution!

[Hi-king]

Cool solution! For workaround, currently we're using __version=IntParameter(default=2) for declaring the change of task definition 💦 This way looks more sophisticated to me !

[hiro-o918]

Thank you for your fast your reviews! :rocket:

[hirosassa]

@hiro-o918 gokart 1.0.1 including your great contribution is released. Thanks again!