move getFeatureFlagsBaseOnAPIFlag from custom_task_test to another file

[Yongxuanzhang]

The getFeatureFlagsBaseOnAPIFlag is used in multiple tests, and when developers want to introduce a new feature flag, they need to change this functions as well.

It's not clear since the helper function is in custom_task_test and also cause confusions to reviewers. We should move it to another file

[Dhruval7878]

If this issue is still open then please assign me

[Yongxuanzhang]

If this issue is still open then please assign me

Thanks!